Method for detecting foreign material, and device and system therefor

ABSTRACT

A wireless power receiver including a transmitter configured to transmit to a wireless power transmitter, a foreign object detection status packet including a mode bit field indicating whether a foreign object detection status packet includes a reference peak frequency of the wireless power receiver, in which the reference peak frequency is pre-assigned to the wireless power receiver; and a receiver configured to receive from the wireless power transmitter, a response indicating the foreign object is present or not present in a charging area of the wireless power transmitter, wherein the response is determined based on a comparison of a measured peak frequency of a power signal transmitted by the wireless power transmitter and an adaptable threshold frequency adapted based on the reference peak frequency included in the foreign object detection status packet from the wireless power receiver.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a Continuation of U.S. patent application Ser. No.16/314,559 filed on Dec. 31, 2018 (now U.S. Pat. No. 11,070,095 issuedon Jul. 20, 2021), which is the National Phase of PCT InternationalApplication No. PCT/KR2017/006975 filed on Jun. 30, 2017, which claimsthe priority benefit under 35 U.S.C. 119(a) to Korean Patent ApplicationNos. 10-2016-0095293 filed on Jul. 27, 2016, 10-2016-0093483 filed onJul. 22, 2016, 10-2016-0090701 filed on Jul. 18, 2016 and10-2016-0083406 filed on Jul. 1, 2016, all filed in the Republic ofKorea, and all of which are hereby expressly incorporated by referenceinto the present application.

BACKGROUND OF THE INVENTION Field of the Invention

Embodiments relate to wireless power transmission technology and, moreparticularly, a method of detecting a foreign object in a wirelesscharging system, and an apparatus and system therefor.

Discussion of the Related Art

Recently, as information and communication technology has been rapidlydeveloped, a ubiquitous society based on information and communicationtechnology is being developed.

In order to connect information communication devices anytime anywhere,sensors equipped with a computer chip having a communication functionshould be installed in all social facilities. Accordingly, supplyingpower to such devices or sensors is a new challenge. In addition, as thetypes of mobile devices such as music players such as Bluetooth handsetsor iPods as well as mobile phones have rapidly increased, it isnecessary for users to take more time and efforts to charge batteries.As a method of solving such problems, wireless power transfer technologyhas recently attracted attention.

Wireless power transmission or wireless energy transfer refers totechnology for wirelessly transmitting electric energy from atransmitter to a receiver using the magnetic induction principle. In1800s, electric motors or transformers using the electromagneticinduction principle have begun to be used and, thereafter, attempts havebeen made to radiate electromagnetic waves such as high frequencies,microwaves and lasers to transfer electric energy. Frequently usedelectric toothbrushes or some wireless shavers are charged using theelectromagnetic induction principle.

Up to now, a wireless energy transfer method may be roughly divided intoa magnetic induction method, an electromagnetic resonance method and aradio frequency (RF) transmission method of a short-wavelength radiofrequency.

The magnetic induction method uses a phenomenon that, when two coils arelocated adjacent to each other and then current is applied to one coil,a magnetic flux is generated to cause an electromotive force in theother coil, and is rapidly being commercialized in small devices such asmobile phones. The magnetic induction method may transfer power of up toseveral hundreds of kilowatts (kW) and has high efficiency. However,since a maximum transmission distance is 1 centimeter (cm) or less, adevice to be charged should be located adjacent to a charger or thefloor.

The electromagnetic resonance method uses an electric field or amagnetic field instead of using electromagnetic waves or current. Theelectromagnetic resonance method is rarely influenced by electromagneticwaves and thus is advantageously safe for other electronic devices orhuman bodies. In contrast, this method may be used in a limited distanceand space and energy transmission efficiency is somewhat low.

The short-wavelength wireless power transmission method (briefly,referred to as the RF transmission method) takes advantage of the factthat energy may be directly transmitted and received in the form of aradio wave. This technology is a RF wireless power transmission methodusing a rectenna. The rectenna is a combination of an antenna and arectifier and means an element for directly converting RF power into DCpower. That is, the RF method is technology of converting AC radio wavesinto DC. Recently, as efficiency of the RF method has been improved,studies into commercialization of the RF method have been activelyconducted

Wireless power transmission technology may be used not only in mobilerelated industries but also in various industries such as IT, railroadand home appliance.

If a conductor which is not a wireless power receiver, that is, aforeign object (FO), is present in a wireless charging area, anelectromagnetic signal received from a wireless power transmitter may beinduced in the FO, thereby increasing in temperature. For example, theFO may include coins, clips, pins, and ballpoint pens.

If an FO is present between a wireless power receiver and a wirelesspower transmitter, wireless charging efficiency may be significantlylowered, and the temperatures of the wireless power receiver and thewireless power transmitter may increase due to increase in ambienttemperature of the FO. If the FO located in the charging area is notremoved, power waste may occur and the wireless power transmitter andthe wireless power receiver may be damaged due to overheating.

Accordingly, accurate detection of the FO located in the charging areais becoming an important issue in wireless charging technology.

SUMMARY OF THE INVENTION

Embodiments provide a method of detecting a foreign object for wirelesscharging, and an apparatus and system therefor.

Embodiments provide a wireless power transmission apparatus capable ofmore accurately detecting a foreign object, by applying a weightdetermined linearly or exponentially according to a reference qualityfactor value and dynamically determining a threshold value or athreshold range for detecting the foreign object.

Embodiments provide a wireless power transmission apparatus capable ofdetecting a foreign object based on a quality factor value and aninductance value of a resonant circuit measured before a ping phase.

Embodiments provide a method of detecting a foreign object, which iscapable of more accurately detecting a foreign object, by measuring aquality factor value and an inductance value of a resonant circuitbefore a ping phase when an object is detected in a charging area andcomparing a determined threshold value with a measured value based on anFOD status packet in a negotiation phase, and an apparatus and systemtherefor. Embodiments provide a wireless power transmitter capable ofdetecting a foreign object based on a quality factor value measured at aspecific frequency in an operating frequency band.

Embodiments provide a wireless power transmitter capable of detecting aforeign object based on a quality factor average value measured at aspecific frequency in an operating frequency band.

The technical problems solved by the embodiments are not limited to theabove technical problems and other technical problems which are notdescribed herein will become apparent to those skilled in the art fromthe following description.

Embodiments provide a method of detecting a foreign object, and anapparatus and system therefor.

In an embodiment, a method of detecting a foreign object in a wirelesspower transmitter including a resonant circuit for wirelesslytransmitting power includes detecting an object placed in a chargingarea, measuring a quality factor value of the resonant circuit when theobject is detected, transmitting a sensing signal to identify a wirelesspower receiver, determining a threshold value for detecting the foreignobject based on a reference quality factor value received from theidentified wireless power receiver, and comparing the measured qualityfactor value with the determined threshold value to determine whetherthe foreign object is present, wherein the threshold value is determinedby applying a weight which increases according to the reference qualityfactor value.

Here, the weight may linearly or exponentially increase according to thereference quality factor value.

In addition, the threshold value may be determined by further applying adesign factor corresponding to the wireless power transmitter and apredefined tolerance, and the threshold value may be determined byadding the tolerance to a product of the reference quality factor valueand the design factor and then subtracting the weight from the addedvalue.

The method may further include starting charging of the identifiedwireless power receiver upon determining that the foreign object is notpresent, and stopping power transfer through the resonant circuit andoutputting a predetermined alarm signal indicating that the foreignobject has been detected, upon determining the foreign object ispresent.

The method may return to the detecting of the object placed in thecharging area when power transfer is stopped.

The method may further include comparing the quality factor value of theresonant circuit measured after returning with the determined thresholdvalue to check whether the foreign object has been removed from thecharging area.

The stopped power transfer may be resumed upon checking that the foreignobject has been removed.

The reference quality factor value may be received in a state of beingincluded in a foreign object detection status packet received in anegotiation phase.

The determining of whether the foreign object is present may includedetermining that the foreign object is not present, when the measuredquality factor value exceeds the threshold value, and determining thatthe foreign object is present, when the measured quality factor value isequal to or less than the threshold value.

According to another embodiment, a method of detecting a foreign objectin a wireless power transmitter including a resonant circuit forwirelessly transmitting power includes detecting an object placed in acharging area, measuring a quality factor value of the resonant circuitwhen the object is detected, transmitting a sensing signal to identify awireless power receiver, determining a threshold range for detecting theforeign object based on a reference quality factor value received fromthe identified wireless power receiver, and comparing the measuredquality factor value with the determined threshold range to determinewhether the foreign object is present, wherein the threshold range isdetermined by applying an upper-limit weight and a lower-limit weightwhich increase according to the reference quality factor value.

According to another embodiment, an apparatus for detecting a foreignobject includes a resonant circuit including a resonant capacitor and aresonant inductor, a sensing unit configured to detect an object placedin a charging area, a measurement unit configured to measure a qualityfactor value of the resonant circuit when the object is detected, and acontroller configured to determine a threshold value for detecting theforeign object based on a reference quality factor value received froman identified wireless power receiver and to compare the measuredquality factor value with the determined threshold value to determinewhether the foreign object is present, wherein the threshold value isdetermined by applying a weight which increases according to thereference quality factor value.

Here, the weight may linearly or exponentially increase according to thereference quality factor value, and the threshold value may bedetermined by adding a predefined tolerance to a product of thereference quality factor value and a design factor corresponding to thewireless power transmitter and then subtracting the weight from theadded value.

In addition, the controller may perform control to start charging of theidentified wireless power receiver upon determining that the foreignobject is not present, and to stop power transfer through the resonantcircuit and to output a predetermined alarm signal indicating that theforeign object has been detected, upon determining the foreign object ispresent.

The controller may return to a selection phase after stopping powertransfer and compare the quality factor value of the resonant circuitmeasured after returning with the determined threshold value to checkwhether the foreign object has been removed from the charging area.

The controller may perform control to resume the stopped power transferupon checking that the foreign object has been removed.

In addition, the apparatus may further include a DC-to-DC converterconfigured to convert DC power from a power supply into specific DCpower and an inverter configured to convert the converted DC power intoAC power, the controller may control the DC-to-DC converter and theinverter to periodically transmit a digital ping for identifying thewireless power receiver when measurement by the measurement unit isterminated, and the wireless power receiver may be identified when asignal strength indicator corresponding to the digital ping is received.

The measurement unit may measure the quality factor value of theresonant circuit based on a voltage measured across the resonantcapacitor.

According to another embodiment, an apparatus for detecting a foreignobject includes a resonant circuit including a resonant capacitor and aresonant inductor, a sensing unit configured to detect an object placedin a charging area, a measurement unit configured to measure a qualityfactor value of the resonant circuit when the object is detected, and acontroller configured to determine a threshold range for detecting theforeign object based on a reference quality factor value received froman identified wireless power receiver and to compare the measuredquality factor value with the determined threshold range to determinewhether the foreign object is present, wherein the threshold range isdetermined by applying an upper-limit weight and a lower-limit weightwhich increase according to the reference quality factor value.

According to another embodiment, a method of detecting a foreign objectin a wireless power transmitter including a resonant circuit forwirelessly transmitting power includes measuring a first inductancevalue of the resonant circuit, receiving a foreign object detectionstatus packet from a wireless power receiver, determining a thresholdvalue for detecting the foreign object based on the foreign objectdetection status packet, and comparing the measured first inductancevalue with the determined threshold value to determine whether theforeign object is present.

In addition, the method may further include detecting an object placedin a charging area and identifying the wireless power receiver, and themeasured first inductance value may include an inductance value of theresonant circuit changed by the detected object.

In addition, the first inductance value may be measured before enteringthe step of identifying the wireless power receiver after detecting theobject.

In addition, the method further include measuring a quality factor valueof the resonant circuit before entering the step of identifying thewireless power receiver after detecting the object.

In addition, the method may further include stopping power transfer tothe wireless power receiver based on the result of determining whetherthe foreign object is present.

In addition, the method may further include correcting power transmittedto the identified wireless power receiver based on the result ofdetermining whether the foreign object is present.

In addition, the method may further include outputting an alarm signalindicating that the foreign object has been detected based on the resultof determining that the foreign object is present.

In addition, the method may further include detecting the object placedin the charging area after stopping the power transfer.

In addition, the method may further include measuring a secondinductance value of the resonant circuit after stopping the powertransfer and comparing the measured second inductance value with thedetermined threshold value to determine whether the detected foreignobject has been removed from the charging area.

In addition, the foreign object detection status packet may include atleast one of a reference quality factor value and a reference inductancevalue.

In addition, the reference inductance value may include the inductancevalue of the resonant circuit measured when the wireless power receiveris located in the charging area without a foreign object.

In one embodiment, the foreign object detection status packet mayfurther include a mode field, and the mode field may include a firstmode indicating that the foreign object detection status packet includesthe reference inductance value.

In another embodiment, the foreign object detection status packet mayfurther include a mode field, and the mode field may include a secondmode indicating that the foreign object detection status packet includesthe reference inductance value and the reference quality factor value.

In addition, the determined threshold value may include a quality factorthreshold value and an inductance threshold value, and the qualityfactor threshold value and the inductance threshold value may includevalues respectively less than the reference quality factor value and thereference inductance value by a predetermined ratio.

In addition, the determined threshold value may include a value greaterthan the reference inductance value by a predetermined ratio.

In addition, the method may further include receiving a received powerstrength packet for correcting the power from the wireless powerreceiver, and the received power strength packet may include receivedpower of the wireless power receiver corresponding to a light load orreceived power of the wireless power receiver corresponding to a loadconnection state.

In addition, the determining of whether the foreign object is presentmay include a first foreign object determination step of comparing themeasured quality factor value with the quality factor threshold value todetermine whether the foreign object is present and a second foreignobject determination step of comparing the measured first inductancevalue with the inductance threshold value to determine whether theforeign object is present.

In addition, upon determining that the foreign object is present in atleast one of the first foreign object determination step and the secondforeign object determination step, it may be finally determined that theforeign object is present.

According to another embodiment, an apparatus for detecting a foreignobject includes a resonant circuit including a resonant capacitor and aresonant inductor, a measurement unit configured to measure a firstinductance value of the resonant circuit and a charging area disposedabove the inductor, and a controller configured to determine a thresholdvalue for detecting the foreign object based on a foreign objectdetection status packet received from a wireless power receiver and tocompare the measured first inductance value with the determinedthreshold value to determine whether the foreign object is present.

In addition, the controller may be configured to detect an objectlocated in the charging area, and the measured first inductance valuemay include the inductance value of the resonant circuit changed by thedetected object.

In addition, the measurement unit may be configured to measure thequality factor value of the resonant circuit, and the measured qualityfactor value may include the quality factor value of the resonantcircuit changed by the detected object.

In addition, the inductance value of the resonant circuit may includethe inductance value of the inductor.

In addition, when the measured first inductance value is greater thanthe determined threshold value, the controller may correct powertransmitted to the wireless power receiver.

In addition, when the measured first inductance value is equal to orless than the determined threshold value, the controller may performcontrol to stop power transfer to the wireless power receiver.

In addition, the foreign object detection status packet may include atleast one of a reference quality factor value and a reference inductancevalue.

In one embodiment, the foreign object detection status packet mayfurther include a mode field, and the mode field may include a firstmode indicating that the foreign object detection status packet includesthe reference inductance value.

In another embodiment, the foreign object detection status packet mayfurther include a mode field, and the mode field may include a secondmode indicating that the foreign object detection status packet includesthe reference inductance value and the reference quality factor value.

In addition, the determined threshold value may include a quality factorthreshold value and an inductance threshold value, and the qualityfactor threshold value and the inductance threshold value may includevalues respectively less than the reference quality factor value and thereference inductance value by a predetermined ratio.

In addition, the determined threshold value may include a value greaterthan the reference inductance value by a predetermined ratio.

In addition, the controller may perform a first foreign objectdetermination of comparing the measured quality factor value with thequality factor threshold value to determine whether the foreign objectis present and a second foreign object determination of comparing themeasured inductance value with the inductance threshold value todetermine whether the foreign object is present.

In addition, upon determining that the foreign object is present in atleast one of the first foreign object determination and the secondforeign object determination, the controller may finally determine thatthe foreign object is present.

In addition, the apparatus may further include a DC-to-DC converterconfigured to convert DC power from a power supply into specific DCpower and an inverter configured to convert the converted DC power intoAC power, the controller may control the DC-to-DC converter and theinverter to periodically transmit a digital ping for identifying thewireless power receiver when measurement by the measurement unit isterminated, and the wireless power receiver may be identified when asignal strength indicator corresponding to the digital ping is received.

In addition, the measurement unit may measure the first inductance valuebased on at least one of a voltage, current and impedance measuredacross the resonant capacitor.

In addition, the measurement unit may include a quality factormeasurement unit configured to calculate the quality factor value basedon the voltage measured across the resonant capacitor and an inductancemeasurement unit configured to calculate the inductance value based onthe voltage and current measured across the inductor.

According to another embodiment, a method of detecting a foreign objectin a wireless power transmitter includes measuring a first qualityfactor value at a first frequency, measuring a second quality factorvalue at a second frequency, and determining whether the foreign objectis present based on the first quality factor value and the secondquality factor value,

For example, the second frequency is greater than the first frequency.When the second quality factor value is greater than the first qualityfactor value, it may be determined that the foreign object is present.

In another example, when the second quality factor value is greater thanthe first quality factor value, it may be determined that a misalignedwireless power receiver is present.

In addition, the method may further include wirelessly transmittingpower according to presence/absence of the foreign object, and thepresence/absence of the foreign object may include presence of theforeign object and absence of the foreign object.

In addition, presence of the foreign object may include a state in whichthe second quality factor value is greater than the first quality factorvalue.

In addition, absence of the foreign object may include a state in whichthe second quality factor value is less than or equal to the firstquality factor value.

In addition, the method may further include outputting a predeterminedalarm signal upon determining that the foreign object is present in thecharging area.

In addition, the method may further include temporarily stopping powertransfer when the foreign object is detected during power transfer.

In addition, the method further includes checking whether the detectedforeign object has been removed from the charging area in a state inwhich the power transfer is temporarily stopped. Upon checking thedetected foreign object has been removed, the temporarily stopped powertransfer may be resumed.

In addition, the method may further include entering a selection phaseafter outputting the alarm signal.

In addition, the method further checks whether the detected foreignobject has been removed from the charging area before entering theselection phase after outputting the alarm signal. Upon checking thedetected foreign object has been removed, the method may enter theselection phase.

In addition, it may be determined that the foreign object is present inthe charging area, when a value obtained by subtracting the firstquality factor value from the second quality factor value exceeds apredetermined reference value.

According to another embodiment, a method of detecting a foreign objectin a wireless power transmitter includes calculating a first qualityfactor average value corresponding to a predetermined upper-limitfrequency band in an operating frequency band, calculating a secondquality factor average value corresponding to a predeterminedlower-limit frequency band in the operating frequency band, anddetermining whether the foreign object is present in a charging area ofthe wireless power transmitter based on the first quality factor averagevalue and the second quality factor average value.

For example, it may be determined that the foreign object is present inthe charging area, when the first quality factor average value isgreater than the second quality factor average value.

In another example, it may be determined that the foreign object ispresent in the charging area, when a value obtained by subtracting thesecond quality factor average value from the first quality factoraverage value exceeds a predetermined reference value.

According to another embodiment, a foreign object detection apparatusprovided in a wireless power transmitter includes a quality factormeasurement unit configured to measure a first quality factor value at afirst frequency in a predetermined operating frequency band and a secondquality factor value at a second frequency in the operating frequencyband, and a detector configured to determine whether a foreign object ispresent in a charging area based on the first quality factor value andthe second quality factor value.

For example, when the second frequency is greater than the firstfrequency and the second quality factor value is greater than the firstquality factor value, the detector may determine that the foreign objectis present in the charging area.

In another example, when the second frequency is greater than the firstfrequency and the second quality factor value is greater than the firstquality factor value, the detector may determine that a misalignedwireless power receiver is present in the charging area.

The foreign object detection apparatus may further include an alarm unitconfigured to output an alarm signal upon determining that the foreignobject is present in the charging area.

The foreign object detection apparatus may further include a controllerconfigured to temporarily stopping power transfer upon determining thatthe foreign object is present in the charging area during powertransfer.

In addition, the controller may check whether the foreign object hasbeen removed from the charging area in a state in which the powertransfer is temporarily stopped, and resume the temporarily stoppedpower transfer upon checking the foreign object has been removed.

The controller may perform control to check whether the foreign objecthas been removed from the charging area before entering the selectionphase after outputting the alarm signal and to enter a selection phaseupon checking that the foreign object has been removed.

In addition, the controller may perform control to check whether thedetected foreign object has been removed from the charging area beforeentering the selection phase after outputting the alarm signal and toenter the selection phase upon checking the foreign object has beenremoved.

In addition, when the second frequency is greater than the firstfrequency and a value obtained by subtracting the first quality factorvalue from the second quality factor value exceeds a predeterminedreference value, the detector may determine that the foreign object ispresent in the charging area.

According to another embodiment, a foreign object detection apparatusprovided in a wireless power transmitter includes a quality factormeasurement unit configured to measure a quality factor value in apredetermined operating frequency band, an average calculator configuredto calculate a first quality factor average value based on at least onequality factor value measured at a predetermined upper-limit frequencyband in the operating frequency band and calculating a second qualityfactor average value based on at least one quality factor value measuredat a predetermined lower-limit frequency band in the operating frequencyband, and a detector configured to determine whether a foreign object ispresent in a charging area of the wireless power transmitter based onthe first quality factor average value and the second quality factoraverage value.

For example, the detector may determine that the foreign object ispresent in the charging area, when the first quality factor averagevalue is greater than the second quality factor average value.

In another example, the detector may determine that a misalignedwireless power receiver is present in the charging area, when a valueobtained by subtracting the second quality factor average value from thefirst quality factor average value exceeds a predetermined referencevalue.

In another embodiment, a computer-readable recording medium havingrecorded thereon a program for executing any one of the above-describedmethods may be provided.

The aspects of the disclosure are only a part of the preferredembodiments of the disclosure, and various embodiments based ontechnical features of the disclosure may be devised and understood bythe person with ordinary skill in the art based on the detaileddescription of the disclosure.

The effects of the method, apparatus and system according to embodimentsare as follows.

Embodiments provide a method of detecting a foreign object for wirelesscharging, and an apparatus and system therefor.

Embodiments provide a method of detecting a foreign object, which iscapable of more accurately detecting a foreign object, and an apparatusand system therefor.

Embodiments may minimize unnecessary power waste and a heatingphenomenon due to a foreign object.

Embodiments provide a wireless power transmission apparatus capable ofmore accurately detecting a foreign object, by applying a weightdetermined linearly or exponentially according to a reference qualityfactor value and dynamically determining a threshold value or athreshold range for detecting the foreign object.

Embodiments provide a wireless power transmission apparatus capable ofdetecting a foreign object based on a quality factor value and aninductance value of a resonant circuit measured before a ping phase.

Embodiments provide a method of detecting a foreign object, which iscapable of more accurately detecting a foreign object, by measuring aquality factor value and an inductance value of a resonant circuitbefore a ping phase when an object is detected in a charging area andcomparing a determined threshold value with a measured value based on anFOD status packet in a negotiation phase, and an apparatus and systemtherefor.

Embodiments provide a method of detecting a foreign object, which iscapable of more accurately detecting the foreign object, by determininga threshold value for dynamically determining whether a foreign objectis present based on a receiver type, and an apparatus and systemtherefor.

Embodiments provide a wireless power transmitter capable of detecting aforeign object based on a quality factor value measured at a specificfrequency in an operating frequency band.

Embodiments provide a wireless power transmitter capable of detecting aforeign object based on a quality factor average value measured at aspecific frequency in an operating frequency band.

Embodiments may minimize foreign object detection errors and thusminimize unnecessary power waste and equipment damage.

The effects of the disclosure are not limited to the above-describedeffects and other effects which are not described herein may be derivedby those skilled in the art from the following description of theembodiments of the disclosure. That is, effects which are not intendedby the disclosure may be derived by those skilled in the art from theembodiments of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a wireless charging systemaccording to an embodiment;

FIG. 2 a is a state transition diagram explaining a wirelesstransmission procedure according to another embodiment;

FIG. 2 b is a graph illustrating the resonance frequency changing with apower receiver on a primary coil;

FIG. 2 c is a graph illustrating the resonance frequency changing withthe power receiver and a foreign object on the primary coil;

FIG. 3 is a block diagram illustrating the structure of a wireless powerreceiver interworking with a wireless power transmitter according to anembodiment;

FIG. 4 is a diagram illustrating a packet format according to anembodiment;

FIG. 5 is a view illustrating the types of packets according to anembodiment;

FIG. 6 a is a block diagram illustrating the structure of a foreignobject detection apparatus according to an embodiment;

FIG. 6 b is a block diagram illustrating the structure of a foreignobject detection apparatus according to another embodiment;

FIG. 7 a is a view illustrating the structure of a foreign objectdetection (FOD) status packet message according to an embodiment;

FIG. 7 b is a view illustrating the structure of an FOD status packetmessage according to an embodiment;

FIG. 7 c is a view illustrating the structure of an FOD status packetmessage according to another embodiment;

FIG. 8 a is a diagram illustrating a status transition procedure forforeign object detection in a foreign object detection apparatusaccording to an embodiment;

FIG. 8 b is a diagram illustrating a status transition procedure forforeign object detection in a foreign object detection apparatusaccording to an embodiment;

FIG. 9 a is a flowchart illustrating a foreign object detection methodin a wireless power transmission apparatus according to anotherembodiment;

FIG. 9 b is a flowchart illustrating a foreign object detection methodin a wireless power transmission apparatus according to anotherembodiment;

FIGS. 10 and 11 are graphs of experimental results showing a degree oflowering a quality factor value as compared to a reference qualityfactor value of each receiver type when a foreign object is placed in acharging area according to an embodiment;

FIG. 12 is a view showing a result of measuring a quality factor valueand an inductance value of a resonant circuit according topresence/absence of a foreign object for each receiver type;

FIG. 13 a is a view illustrating the structure of an FOD status packetmessage according to another embodiment;

FIG. 13 b is a view illustrating the structure of an FOD status packetmessage according to another embodiment;

FIG. 13 c is a view illustrating the structure of an FOD status packetmessage according to another embodiment;

FIGS. 13 d to 13 g are views illustrating the structure of an FOD statuspacket message according to an embodiment;

FIG. 14 is a flowchart illustrating an FOD method according to anotherembodiment;

FIG. 15 is a flowchart illustrating an FOD method according to anotherembodiment;

FIG. 16 is a quality factor table according to an embodiment;

FIG. 17 is a block diagram illustrating the configuration of an FOdetection apparatus according to an embodiment;

FIG. 18 is a flowchart illustrating an FOD method according to anotherembodiment;

FIG. 19 is a flowchart illustrating an FOD method according to anotherembodiment;

FIG. 20 is a flowchart illustrating an FOD method based on a qualityfactor value according to another embodiment;

FIG. 21 is a block diagram illustrating the structure of an FODapparatus corresponding to the embodiment of FIG. 20 ;

FIG. 22 is a flowchart illustrating an FOD method based on a qualityfactor value according to another embodiment;

FIG. 23 is a block diagram illustrating the structure of an FODapparatus corresponding to the embodiment of FIG. 22 ;

FIGS. 24 a to 24 e are graphs of experimental results illustrating alogical basis of the embodiments of FIGS. 14 to 23 .

FIG. 25 is a view illustrating a relationship between a quality factorvalue and a maximum quality factor peak frequency according to placementof a foreign object and a wireless power receiver in a charging area ofa wireless power transmitter;

FIG. 26 is a view illustrating a state transition procedure fordetecting a foreign object in a foreign object detection apparatusaccording to an embodiment;

FIG. 27 is a view illustrating the structure of an FOD status packetmessage according to another embodiment;

FIG. 28 is a view illustrating a state transition procedure fordetecting a foreign object in a foreign object detection apparatusaccording to an embodiment;

FIG. 29 is a view illustrating a state transition procedure fordetecting a foreign object in a foreign object detection apparatusaccording to an embodiment; and

FIG. 30 is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

A method of detecting a foreign object in a wireless power transmitterincluding a resonant circuit for wirelessly transmitting power includesdetecting an object placed in a charging area, measuring a qualityfactor value of the resonant circuit when the object is detected,transmitting a sensing signal to identify a wireless power receiver,determining a threshold value for detecting the foreign object based ona reference quality factor value received from the identified wirelesspower receiver, and comparing the measured quality factor value with thedetermined threshold value to determine whether the foreign object ispresent, wherein the threshold value is determined by applying a weightwhich increases according to the reference quality factor value.

Hereinafter, apparatuses and various methods according to embodimentswill be described in detail with reference to the accompanying drawings.In general, a suffix such as “module” or “unit” may be used to refer toelements or components. Use of such a suffix herein is merely intendedto facilitate description of the specification, and the suffix itself isnot intended to have any special meaning or function.

In the following description of the embodiments, it will be understoodthat, when each element is referred to as being formed “on” or “under”the other element, it can be directly “on” or “under” the other elementor be indirectly formed with one or more intervening elementstherebetween. In addition, it will also be understood that “on” or“under” the element may mean an upward direction and a downwarddirection of the element.

In the description of embodiments, an apparatus having a function fortransmitting wireless power in a wireless charging system may be usedinterchangeably with a wireless power transmitter, a wireless powertransfer apparatus, a wireless electric power transfer apparatus, awireless electric power transmitter, a transmission end, a transmitter,a transmission apparatus, a transmission side, a wireless power transferapparatus, a wireless power transferer, etc., for convenience ofdescription. An apparatus having a function for receiving wireless powerfrom a wireless power transfer apparatus may be used interchangeablywith a wireless electric power reception apparatus, a wireless electricpower receiver, a wireless power reception apparatus, a wireless powerreceiver, a reception terminal, a reception side, a reception apparatus,a receiver, etc.

The transmitter according to embodiment may be configured in the form ofa pad, a cradle, an access point (AP), a small base station, a stand, aceiling embedded structure or a wall-mounted structure. One transmittermay transfer power to a plurality of wireless power receptionapparatuses. To this end, the transmitter may include at least onewireless power transfer means. Here, the wireless power transfer meansmay use various wireless power transfer standards based on anelectromagnetic induction method of performing charging using theelectromagnetic induction principle in which a magnetic field isgenerated in a power transfer-end coil and electricity is induced in areception-end coil by the magnetic field. Here, the wireless powertransfer means may include wireless charging technology of theelectromagnetic induction method defined in the Wireless PowerConsortium (WPC) and Power Matters Alliance (PMA) which are the wirelesscharging technology organizations.

In addition, a receiver according to an embodiment may include at leastone wireless power reception means and may simultaneously receivewireless power from two or more transmitters. Here, the wireless powerreception means may include wireless charging technology of theelectromagnetic induction method defined in the Wireless PowerConsortium (WPC) and Power Matters Alliance (PMA) which are the wirelesscharging technology organizations.

The receiver according to the embodiment may be used in a smallelectronic apparatus such as a mobile phone, a smartphone, a laptop, adigital broadcast terminal, a personal digital assistant (PDA), aportable multimedia player (PMP), a navigation system, an MP3 player, anelectric toothbrush, an electronic tag, a lighting device, a remotecontroller, a fishing float, a wearable device such as a smart watch,etc. without being limited thereto, and may be used in any apparatusincluding wireless power reception means according to embodiment tocharge a battery.

FIG. 1 is a block diagram illustrating a wireless charging systemaccording to an embodiment.

Referring to FIG. 1 , the wireless charging system roughly includes awireless power transfer end 10 for wirelessly transmitting power, awireless power reception end 20 for receiving the transmitted power andan electronic apparatus 30 for receiving the received power.

For example, the wireless power transfer end 10 and the wireless powerreception end 20 may perform in-band communication in which informationis exchanged using the same frequency band as the operating frequencyused for wireless power transfer.

In in-band communication, when a power signal 41 transmitted by thewireless power transfer end 10 is received by the wireless powerreception end 20, the wireless power reception end 20 may modulate thereceived power signal and transmit a modulated signal 42 to the wirelesspower transfer end 10.

In another example, the wireless power transfer end 10 and the wirelesspower reception end 20 may perform out-of-band communication in whichinformation is exchanged using the frequency band different from theoperating frequency used for wireless power transfer.

For example, the information exchanged between the wireless powertransfer end 10 and the wireless power reception end 20 may includestatus information of each other and control information. Here, thestatus information and the control information exchanged between thetransmission end and the reception end will become more apparent throughthe following description of the embodiments.

In-band communication and out-of-communication may provide bidirectionalcommunication, but the embodiments are not limited thereto. In anotherembodiment, in-band communication and out-of-communication may provide aunidirectional communication or half duplex communication.

For example, unidirectional communication may, but is not limited to,mean transmission of information from the wireless power reception end20 to the wireless power transfer end 10 or transmission from thewireless power transfer end 10 to the wireless power reception end 20.

The half duplex communication method is characterized in thatbidirectional communication between the wireless power reception end 20and the wireless power transfer end 10 is enabled but information can betransmitted only by one device at a certain point in time.

The wireless power reception end 20 according to the embodiment mayacquire a variety of status information of the electronic apparatus 30.For example, the status information of the electronic apparatus 30 mayinclude, but is not limited to, current power usage information, currentpower usage information, information for identifying an executedapplication, CPU usage information, battery charge status information,battery output voltage/current information, etc. and may includeinformation capable of being acquired from the electronic apparatus 30and being used for wireless power control.

In particular, the wireless power transfer end 10 according to theembodiment may transmit a predetermined packet indicating whether fastcharging is supported to the wireless power reception end 20. Thewireless power reception end 20 may inform the electronic apparatus 30that the wireless power transfer end 10 supports the fast charging mode,upon determining that the wireless power transfer end 10 supports thefast charging mode. The electronic apparatus 30 may display informationindicating that fast charging is possible through a predetermineddisplay means, for example, a liquid crystal display.

In addition, the user of the electronic apparatus 30 may select apredetermined fast charging request button displayed on the liquidcrystal display means and control the wireless power transmission end 10to operate in the fast charging mode. In this case, when the userselects the fast charging request button, the electronic apparatus 30may transmit a predetermined fast charging request signal to thewireless power reception end 20. The wireless power reception end 20 maygenerate and transmit a charging mode packet corresponding to thereceived fast charging request signal to the wireless power transmissionend 10, thereby switching a normal low-power charging mode to the fastcharging mode.

FIG. 2 a is a state transition diagram explaining a wirelesstransmission procedure according to another embodiment.

Referring to FIG. 2 a , power transfer from the transmitter to thereceiver may be broadly divided into a selection phase 210, a ping phase220, an identification and configuration phase 230, a negotiation phase240, a calibration phase 250, a power transfer phase 260 and arenegotiation phase 270.

The selection phase 210 may transition when power transfer starts orwhen a specific error or a specific event is detected while powertransfer is maintained. The specific error and the specific event willbecome apparent from the following description. In addition, in theselection phase 210, the transmitter may monitor whether an object ispresent on an interface surface. Upon detecting that the object ispresent on the interface surface, the transmitter may transition to theping step 220. In the selection phase 210, the transmitter transmits ananalog ping signal having a very short pulse and detects whether anobject is present in an active area of the interface surface based oncurrent change of a transmission coil or a primary coil.

In one embodiment, when the object is detected in the selection phase210, the quality factor value may be measured in order to determinewhether the wireless power receiver is placed in the charging area alongwith the foreign object. The inductance and/or series resistancecomponent in the coil of the wireless power transmitter may be reducedaccording to environmental change and thus the quality factor may bereduced. In order to determine whether a foreign object is present usingthe measured quality factor, the wireless power transmitter may receive,from the wireless power receiver, a reference quality factor valuemeasured in advance in a state in which a foreign object is not present.(Negotiation phase 240) The received reference quality factor value andthe measured quality factor value may be compared to determine whether aforeign object is present. However, in the case of a wireless powerreceiver having a low reference quality factor value (the wireless powerreceiver may have a low reference quality factor according to thecharacteristics of the wireless power receiver), since the qualityfactor value measured when the foreign object is present is notsignificantly changed, it may be difficult to determine whether aforeign object is present. Accordingly, it is necessary to determinewhether a foreign object is present by further considering anotherdetermination element or using another method.

In another embodiment, when the object is detected in the selectionphase 210, the quality factor value within a specific frequency region(e.g., an operating frequency region) may be measured in order todetermine whether the wireless power receiver is placed in the chargingarea along with a foreign object. The inductance and/or seriesresistance component in the coil of the wireless power transmitter maybe reduced according to environmental change and thus the resonantfrequency of the coil of the wireless power transmitter may be changed(shifted). That is, the quality factor peak frequency, at which amaximum quality factor is measured, may be moved.

For example, since the wireless power receiver includes a magneticshield (a shielding material) having high permeability, the highpermeability may increase the inductance value measured in the coil ofthe wireless power transmitter. In contrast, a foreign object formed ofa metal material may reduce inductance.

For example, when the resonant frequency of the coil of the wirelesspower transmitter is 100 kHz, the graph of the quality factor measuredwhen the wireless power receiver or the foreign object is placed in thecharging area is changed as shown in FIGS. 2 b and 2 c.

In the case of the wireless power receiver, since the L value isincreased, the resonant frequency is decreased and moved (shifted) tothe left on the frequency axis.

In the case of the foreign object, since the L value is decreased, theresonant frequency is increased and moved (shifted) to the right on thefrequency axis.

In order to determine whether a foreign object is present using themeasured maximum quality factor peak frequency (measured peakfrequency), the wireless power transmitter may receive, from thewireless power receiver, the reference maximum quality factor frequency(reference peak frequency) value measured in advance in a state in whicha foreign object is not present. (Negotiation phase 240) The receivedreference peak frequency value and the measured peak frequency value maybe compared to determine whether a foreign object is present.

This method may be used along with the quality factor value comparisonmethod. When there is no significant difference between the referencequality factor value and the measured quality factor value as the resultof comparison (e.g., a difference of 10% or less (for reference, it maybe immediately determined that a foreign object is present when thedifference exceeds 10%)), the reference peak frequency and the measuredpeak frequency may be compared to determine the foreign object. Thedetailed comparison method will be described in the below-describedembodiments of FIGS. 1 to 30 .

In the ping step 220, when the object is detected, the transmitteractivates the receiver and transmits a digital ping for identifyingwhether the receiver is compatible with the WPC standard. In the pingstep 220, when a response signal to the digital ping, for example, asignal strength packet, is not received from the receiver, thetransmitter may transition to the selection phase 210 again. Inaddition, in the ping phase 220, when a signal indicating that powertransfer has been terminated, that is, a charging termination packet, isreceived from the receiver, the transmitter may transition to theselection phase 210.

If the ping phase 220 is terminated, the transmitter may transition tothe identification and configuration phase 230 for identifying thereceiver and collecting the configuration and status information of thereceiver.

In the identification and configuration phase 230, when an unexpectedpacket is received, when an expected packet is not received during apredetermined time (timeout), when a packet transmission error occurs,or when power transfer contract is not established (no power transfercontract), the transmitter may transition to the selection phase 210.

The transmitter may determine whether entry into the negotiation phase240 is necessary based on the negotiation field value of theconfiguration packet received in the identification and configurationphase 230.

Upon determining that negotiation is necessary, the transmitter mayenter the negotiation phase 240 to perform a predetermined FODprocedure.

In contrast, upon determining that negotiation is not necessary, thetransmitter may immediately transition to the power transfer phase 260.

In the negotiation phase 240, the transmitter may receive a foreignobject detection (FOD) status packet including a reference qualityfactor value. At this time, the transmitter may determine a thresholdvalue for FO detection based on the reference quality factor value.

For example, the transmitter may determine a threshold value or athreshold range for determining whether a foreign object is presentusing a predetermined threshold generation function using a referencequality factor value as a parameter. Here, the threshold value orthreshold range calculated by the threshold generation function is lessthan the reference quality factor value. The threshold valueFO_Threshold for detecting the foreign object according to an embodimentmay be determined based on a reference quality factor value RQF_Value, apredetermined design factor Design_factor corresponding to the wirelesspower transmitter, a tolerance defined in the standard, and a weight.Here, the weight may linearly or exponentially increase according to thereference quality factor value. That is, the threshold value fordetecting the foreign object may be determined by Equation 1:FO_Threshold=(RQF_Value*Design_factor)+tolerance−weight  (Equation 1)

In general, if a foreign object is placed in a charging area, thequality factor value measured in the resonant circuit of the transmitteris lowered as compared to the case where the foreign object is notpresent. If the foreign object is placed in the charging area in anactual wireless charging system, a rate at which the measured qualityfactor value is reduced relative to the reference quality factor valuemay vary according to the type of the receiver placed in the chargingarea, that is, the reference quality factor value of the wireless powerreceiver. In particular, as the reference quality factor valueincreases, the decrease rate of the quality factor value due toplacement of the foreign object rapidly increases. Accordingly, thetransmitter according to the present invention may determine thethreshold value (or the threshold range) such that the ratio of thethreshold value for detecting the foreign object to the referencequality factor value decreases as the reference quality factor value ofthe wireless power receiver increases. As a result, it is possible toreduce a probability that the transmitter fails to detect the foreignobject.

The transmitter may compare the quality factor value measured afterdetecting an object with the threshold value determined for FO detectionto determine whether the FO is present in the charging area, and controlpower transfer according to the FO detection result. For example, whenthe FO is detected, the transmitter may stop power transfer and output apredetermined warning alarm indicating that the FO has been detected.

When the FO is detected, the transmitter may return to the selectionphase 210. In contrast, when the FO is not detected, the transmitter maytransition to the power transfer phase 260 through the calibration phase250. Specifically, when the FO is not detected, the transmitter maymeasure power loss in the reception end and the transmission end, inorder to determine the strength of the power received by the receptionend and to determine the strength of the power transmitted by thetransmission end in the calibration phase 250. That is, the transmittermay predict power loss based on a difference between the transmissionpower of the transmission end and the reception power of the receptionend in the calibration phase 250. The transmitter according to oneembodiment may calibrate the threshold value for FOD using the predictedpower loss.

In the power transfer phase 260, when an unexpected packet is received,when an expected packet is not received during a predetermined time(timeout), when power transfer contract violation occurs or whencharging is terminated, the transmitter may transition to the selectionphase 210.

In addition, in the power transfer phase 260, if a power transfercontract needs to be reconfigured according to transmitter statuschange, etc., the transmitter may transition to the renegotiation phase270. At this time, when renegotiation is normally terminated, thetransmitter may return to the power transfer phase 260.

The power transfer contract may be configured based on the transmitterand receiver status information and characteristic information. Forexample, the transmitter status information may include information onthe maximum amount of transmittable power, information on the maximumnumber of receivable receivers, etc. and the receiver status informationmay include information on required power.

FIG. 3 is a block diagram illustrating the structure of a wireless powerreceiver interworking with the wireless power transmitter.

Referring to FIG. 3 , the wireless power receiver 300 may include atleast one of a reception coil 310, a rectifier 320, a DC-to-DC converter330, a load 340, a sensing unit 350, a communication unit 360, and amain controller 370. The communication unit 360 may include ademodulator 361 and a modulator 362.

Although the wireless power receiver 300 shown in the example of FIG. 3is shown as exchanging information with the wireless power transmitter600 through in-band communication, this is merely an example and thecommunication unit 360 according to another embodiment may provideshort-range bidirectional communication through a frequency banddifferent from a frequency band used to transmit a wireless powersignal.

AC power received through the reception coil 310 may be transmitted tothe rectifier 320. The rectifier 320 may convert the AC power into DCpower and transmit the DC power to the DC-to-DC converter 330. TheDC-to-DC converter 330 may convert the strength of the DC power outputfrom the rectifier into a specific strength required by the load 340 andtransmit the converted power to the load 340.

The sensing unit 350 may measure the strength of the DC power outputfrom the rectifier 320 and provide the strength to the main controller370. In addition, the sensing unit 350 may measure the strength ofcurrent applied to the reception coil 310 according to wireless powerreception and transmit the measured result to the main controller 370.In addition, the sensing unit 350 may measure the internal temperatureof the wireless power receiver 300 and provide the measured temperaturevalue to the main controller 370.

For example, the main controller 370 may compare the strength of the DCpower output from the rectifier with a predetermined reference value anddetermine whether overvoltage occurs. Upon determining that overvoltageoccurs, a predetermined packet indicating that overvoltage has occurredmay be generated and transmitted to the modulator 362. The signalmodulated by the modulator 362 may be transmitted to the wireless powertransmitter 600 through the reception coil 310 or a separate coil (notshown). If the strength of the DC power output from the rectifier isequal to or greater than the predetermined reference value, the maincontroller 370 may determine that a sensing signal is received andperform control to transmit a signal strength indicator corresponding tothe sensing signal to the wireless power transmitter 600 through themodulator 362 upon receiving the sensing signal. In another example, thedemodulator 361 may demodulate the AC power signal between the receptioncoil 310 and the rectifier 320 or the DC power signal output from therectifier 320, identify whether a sensing signal is received, andprovide the identified result to the main controller 370. At this time,the main controller 370 may perform control to transmit the signalstrength indicator corresponding to the sensing signal through themodulator 362.

FIG. 4 is a view illustrating a packet format according to anembodiment.

Referring to FIG. 4 , the packet format 400 used for informationexchange between the wireless power transfer end 10 and the wirelesspower reception end 20 may include a preamble 410 field for acquiringsynchronization for demodulation of the corresponding packet andidentifying an accurate start bit of the corresponding packet, a header420 field for identifying the type of a message included in thecorresponding packet, a message 430 field for transmitting the content(or payload) of the corresponding packet, and a checksum 440 field foridentifying whether an error has occurred in the corresponding packet.

A packet reception end may identify the size of the message 430 includedin the corresponding packet based on the value of the header 420.

In addition, the header 420 may be defined for each step of the wirelesspower transfer procedure, and the value of the header 420 may be definedas the same value in different phases of the wireless power transferprocedure. For example, referring to FIG. 10 , it should be noted thatthe header value corresponding to end power transfer of the ping phaseand end power transfer of the power transfer phase is 0x02.

The message 430 includes data to be transmitted by the transmission endof the corresponding packet. For example, the data included in themessage 430 field may be a report, a request, or a response, withoutbeing limited thereto.

The packet 400 according to another embodiment may further include atleast one of transmission end identification information for identifyingthe transmission end for transmitting the corresponding packet andreception end identification information for identifying the receptionend for receiving the corresponding packet. The transmission endidentification information and the reception end identification mayinclude IP address information, MAC address information, productidentification information, etc. However, the present disclosure is notlimited thereto and information for distinguishing the reception end andthe transmission end in the wireless charging system may be included.

The packet 400 according to another embodiment may further includepredetermined group identification information for identifying areception group if the corresponding packet is received by a pluralityof apparatuses.

FIG. 5 is a view illustrating the types of packets transmitted from thewireless power receiver to the wireless power transmitter according toan embodiment.

Referring to FIG. 5 , the packet transmitted from the wireless powerreceiver to the wireless power transmitter may include a signal strengthpacket for transmitting the strength information of a sensed pingsignal, a power transfer type (end power transfer) for requesting powertransfer end from the transmitter, a power control hold-off packet fortransferring information on a time waiting until actual power iscontrolled after a control error packet for control is received, aconfiguration packet for transferring configuration information of thereceiver, an identification packet and an extended identification packetfor transmitting receiver identification information, a general requestpacket for transmitting a general request message, a specific requestpacket for transmitting a specific request message, an FOD status packetfor transmitting a reference quality factor value for FO detection, acontrol error packet for controlling power transmitted by thetransmitter, a renegotiation packet for starting renegotiation, a 24-bitreceived power packet for transmitting the strength information of thereceived power, and a charge status packet for transmitting the currentcharging status information of the load.

The packets transmitted from the wireless power receiver to the wirelesspower transmitter may be transmitted using in-band communication usingthe same frequency band as the frequency band used to transmit wirelesspower.

FIG. 6 a is a block diagram illustrating the structure of a foreignobject detection apparatus according to an embodiment.

Referring to FIG. 6 a , a foreign object detection apparatus 600 mayinclude a power supply 601, a DC-to-DC converter 610, an inverter 620, aresonant circuit 630, a measurement unit 640, a communication unit 660,a sensing unit 670 and a controller 680. The foreign object detectionapparatus 600 may be mounted in the wireless power transmissionapparatus.

The resonant circuit 630 may include a resonant capacitor 631 and aresonant inductor 632, and the communication unit 660 may include atleast one of a demodulator 661 and a modulator 662.

The power supply 601 may receive DC power through an external powerterminal and transmit the DC power to the DC-to-DC converter 610.

The DC-to-DC converter 610 may convert the strength of the DC powerreceived from the power supply 601 into a specific strength of DC powerunder control of the controller 680. For example, the DC-to-DC converter610 may include a variable voltage generator capable of adjusting thestrength of the voltage, without being limited thereto.

The inverter 620 may convert the converted DC power into AC power. Theinverter 620 may convert the DC power signal input through control of aplurality of switches into an AC power signal and output the AC powersignal.

For example, the inverter 620 may include a full bridge circuit.However, the present disclosure is not limited thereto and the invertermay include a half bridge circuit.

In another example, the inverter 620 may include a half bridge circuitand a full bridge circuit. In this case, the controller 680 maydynamically determine whether the inverter 620 operates as a half bridgeor a full bridge.

The wireless power transmission apparatus according to one embodimentmay adaptively control the bridge mode of the inverter 620 according tothe strength of the power required by the wireless power receptionapparatus. Here, the bridge mode includes a half bridge mode and a fullbridge mode.

For example, if the wireless power reception apparatus requests lowpower of 5 W, the controller 680 may perform control such that theinverter 620 is driven in the half bridge mode. In contrast, if thewireless power reception apparatus requests high power of 15 W, thecontroller 680 may perform control such that the inverter is driven inthe full bridge mode.

In another example, the wireless power transmission apparatus mayadaptively determine the bridge mode according to a sensed temperatureand drive the inverter 620 in the determined bridge mode. For example,if the temperature of the wireless power transmission apparatus exceedsa predetermined reference value while wireless power is transmittedusing the half bridge mode, the controller 680 may perform control todeactivate the half bridge mode and activate the full bridge mode. Thatis, the wireless power transmission apparatus may increase the voltageand decrease the strength of current flowing in the resonant circuit 630through the full bridge circuit for transmission of power having thesame strength, thereby maintaining the internal temperature of thewireless power transmission apparatus at a reference value or less.

In general, the amount of heat generated in an electronic part mountedin the electronic apparatus may be more sensitive to the strength ofcurrent than the strength of the voltage applied to the electronic part.

In addition, the inverter 620 may not only convert the DC power into ACpower but also change the strength of the AC power.

For example, the inverter 620 may adjust the strength of the output ACpower by adjusting the frequency of a reference alternating currentsignal used to generate the AC power under control of the controller680. To this end, the inverter 620 may include a frequency oscillatorfor generating the reference alternating current signal having aspecific frequency. However, this is merely an example and the frequencyoscillator may be mounted independently of the inverter 620 and mountedat one side of the foreign object detection apparatus 600.

In another example, the foreign object detection apparatus 600 mayfurther include a gate driver (not shown) for controlling the switchprovided in the inverter 620. In this case, the gate driver may receiveat least one pulse width modulation signal from the controller 680 andcontrol the switch of the inverter 620 according to the received pulsewidth modulation signal. The controller 680 may control the duty cycle,that is, the duty rate, and phase of the pulse width modulation signalto control the strength of the output power of the inverter 620. Thecontroller 680 may adaptively control the duty cycle and phase of thepulse width modulation signal based on the feedback signal received fromthe wireless power reception apparatus.

The measurement unit 640 may measure at least one of a voltage, currentand impedance across the resonant capacitor 631 according to the controlsignal of the controller 680 to calculate the quality factor valueand/or inductance value of the resonant circuit 630. At this time, thecalculated quality factor value and/or inductance value may be sent tothe controller 680, and the controller 680 may temporarily store thequality factor value and/or the inductance value received from themeasurement unit 640 in a predetermined recording region. For example,when an object is detected in the charging area in the selection phase,the controller 680 may control the measurement unit 640 to calculate thequality factor value and/or the inductance value before entering theping phase.

When the FOD status packet is received from the modulator 662 in thenegotiation phase, the controller 680 may determine a threshold value(or a threshold range) for determining whether a foreign object ispresent based on information included in the FOD status packet.

The threshold value FO_Threshold for detecting the foreign objectaccording to an embodiment may be determined based on a referencequality factor value RQF_Value, a predetermined design factorDesign_factor corresponding to the wireless power transmitter, atolerance defined in the standard, and a weight. Here, the weight maylinearly or exponentially increase according to the reference qualityfactor value. That is, the controller 680 may determine the thresholdvalue for detecting the foreign object by Equation 1:FO_Threshold=(RQF_Value*Design_factor)+tolerance−weight  (Equation 1)

For example, although the weight may be calculated by a predeterminedlinear function using a reference quality factor value as a parameter,the embodiment is not limited thereto and the weight may be calculatedby a higher-order function such as a second-order function or higher.

In another example, the weight may be predefined for each wireless powerreceiver type and recorded and maintained in the predetermined recordingregion, for example, a nonvolatile memory, of the foreign objectdetection apparatus 600. At this time, the weight of each wireless powerreceiver type may be maintained in the form of a mapping table, withoutbeing limited thereto.

The threshold range for detecting the foreign object according toanother embodiment is identified by an upper-limit threshold valueFO_Theshold_Upper_Limit and a lower-limit threshold valueFO_Theshold_Lower_Limit, and may be determined based on a referencequality factor value RQF_Value, a predetermined design factorDesign_factor corresponding to the wireless power transmitter, atolerance defined in the standard, an upper-limit weight and alower-limit weight. Here, the upper-limit weight and the lower-limitweight may linearly or exponentially increase according to the referencequality factor value. That is, the controller 680 may determine thethreshold range for detecting the foreign object by Equation 2:FO_Threshold_Upper_Limit=(RQF_Value*Design_factor)+tolerance−upper-limitweightFO_Threshold_Lower_Limit=(RQF_Value*Design_factor)+tolerance−lower-limitweight   (Equation 2)

The controller 680 may determine that a foreign object is present, ifthe measured quality factor value is between the upper-limit thresholdvalue and the lower-limit threshold value.

The threshold value FO_Threshold for detecting the foreign objectaccording to another embodiment may be determined by applying adifferential (Diff) ratio according to the reference quality factor(RQF) value, as shown in Table 1 below.

For example, referring to Table 1 below, when the RQF value exceeds 80,the Diff ratio of 40% is applied. At this time, the threshold valueFO_Threshold for detecting the foreign object may be calculated byRQF×0.6+tolerance.

In another example, referring to Table 1 below, if the RQF value isgreater than or equal to 50 and is less than or equal to 60, the DiffRatio of 10% is applied. At this time, the threshold value FO_Thresholdfor detecting the foreign object may be calculated by RQF×0.9+tolerance.

TABLE 1 Reference quality factor (RQF) Diff ratio FO_Threshold >80 40%=RQF × 0.6 + tolerance 80 ≥ RQF ≥ 70 30% =RQF × 0.7 + tolerance 70 ≥ RQF≥ 60 20% =RQF × 0.8 + tolerance 60 ≥ RQF ≥ 50 10% =RQF × 0.9 + tolerance50 ≥ RQF  5% =RQF × 0.95 + tolerance

The wireless power transmitter may receive the reference quality factorvalue through the FOD status packet in the negotiation phase andadaptively determine FO_Threshold according to the received referencequality factor value. As shown in Table 1 above, as the RQF valueincreases, a difference between the RQF value and FO_Threshold increasesaccording to the Diff ratio corresponding to the RQF value. In contrast,as the RQF value decreases, a difference between the RQF value andFO_Threshold decreases according to the Diff ratio corresponding to theRQF value. It should be noted that Table 1 above is only an example andthe Diff ratio according to the RQF value may be differently determinedaccording to the design of those skilled in the art and theconfiguration of the device.

In general, if a foreign object is placed in a charging area, thequality factor value measured in the resonant circuit of the transmitteris lowered as compared to the case where the foreign object is notpresent. If the foreign object is placed in the charging area in anactual wireless charging system, a rate at which the measured qualityfactor value is reduced relative to the reference quality factor valuemay vary according to the type of the receiver placed in the chargingarea, that is, the reference quality factor value of the wireless powerreceiver.

In particular, as the reference quality factor value increases, thedecrease rate of the quality factor value due to placement of theforeign object rapidly increases. Accordingly, the controller 680according to the present invention may determine the threshold value (orthe threshold range) such that the ratio of the threshold value fordetecting the foreign object to the reference quality factor valuedecreases as the reference quality factor value of the wireless powerreceiver increases. As a result, it is possible to reduce a probabilitythat the transmitter fails to detect the foreign object.

The controller 680 may compare the quality factor value measured afterdetecting an object with the threshold value determined for FO detectionto determine whether the FO is present in the charging area, and controlpower transfer according to the FO detection result.

For example, when the FO is detected, the controller 680 may stop powertransfer, and perform control to output a predetermined warning alarmindicating that the FO has been detected. Here, the warning alarm may beoutput through at least one of a beeper, an LED lamp, a vibrationelement and a liquid crystal display provided in the foreign objectdetection apparatus, without being limited thereto.

For example, if the quality factor value measured before entering theping phase after detecting the object in the selection phase is lessthan the determined threshold value, the controller 680 may determinethat the foreign object is present in the charging area.

In another example, if the quality factor value measured before enteringthe ping phase after detecting the object in the selection phase isincluded in the determined threshold range, the controller 680 maydetermine that the foreign object is present in the charging area.

The reference quality factor value included in the FOD status packet maybe determined to be the smallest value of the quality factor valuescalculated in correspondence with the wireless power receiver at aspecific position of a charging bed of a wireless power transmitterspecified for standard performance test.

In addition, if the foreign object is detected in the negotiation phase,the controller 680 may return to the selection phase and control themeasurement unit 640 to calculate the quality factor value of theresonant circuit 630 at predetermined periods.

At this time, the controller 680 may compare the quality factor valueacquired in a state of detecting the foreign object with a predeterminedthreshold value (or a threshold range) to determine whether the detectedforeign object has been removed from the charging area.

For example, the controller 680 may determine that the foreign objecthas been removed, if the quality factor value measured in the state inwhich the foreign object is detected is greater than a predeterminedthreshold value. In another example, the controller 680 may determinethat the foreign object has been removed, if the quality factor valuemeasured in the state in which the foreign object is detected exceeds anupper-limit threshold value.

In addition, the controller 680 may adaptively determine the thresholdvalue for detecting the foreign object by referring to Table 1 above(referred to as a “threshold value determination table”, for convenienceof description).

Table 1 above may be maintained in the predetermined recording region ofthe memory (not shown) provided in the foreign object detectionapparatus 600. When the FOD status packet including the referencequality factor value is received in the negotiation phase, thecontroller 680 may determine the threshold value for detecting theforeign object by referring to the received reference quality factorvalue and the threshold value determination table, and compare thedetermined threshold value with the pre-measured quality factor value todetermine whether the foreign object is present.

Here, the threshold value determination table may be updated. Forexample, the foreign object detection apparatus may be connected to aspecific server through a wired or wireless network and interwork withthe server to update the threshold value determination table. In anotherexample, the foreign object detection apparatus may receive or updatethe threshold value determination table from the connected wirelesspower receiver.

The threshold value determination table may be generated according tothe type of the wireless power receiver, and the foreign objectdetection apparatus may determine the threshold value for detecting theforeign object by referring to the threshold value determination tablecorresponding to the type of the identified wireless power receiver.

In the wireless power receiver according to the embodiment, thethreshold value determination table generated according to the type ofthe wireless power transmitter may be maintained. In this case, thewireless power receiver may transmit the threshold value determinationtable corresponding to the type of the identified wireless powertransmitter to the wireless power transmitter. The wireless powertransmitter may determine the threshold value for detecting the foreignobject based on the received threshold value determination table.

As described above, the foreign object detection apparatus according tothe embodiment may adaptively determine the threshold value fordetecting the foreign object by referring to at least one of the type ofthe wireless power receiver and the threshold value determination tablecorresponding to the type of the wireless power transmitter.

Upon determining that the foreign object has been removed, thecontroller 680 may perform control to enter the power transfer phaseagain to resume charging of the wireless power reception apparatus.

In addition, the threshold value may include an inductance thresholdvalue and a quality factor threshold value. If the determined value is athreshold range, the threshold range may include the inductancethreshold range and the quality factor threshold range. The foreignobject may be detected using the two threshold values, or the thresholdvalue corresponding to the type may be determined according to the typeof the reference value transmitted by each receiver to detect theforeign object.

Here, the FOD status packet may include at least one of a referencequality factor value and a reference inductance value corresponding tothe wireless power receiver. The controller 680 may determine thequality factor threshold value and/or the inductance threshold value fordetermining whether the foreign object is present based on the receivedreference quality factor value and the reference inductance value. Forexample, although a value corresponding to 90% of the reference qualityfactor value and the reference inductance value may be determined as thequality factor threshold value and/or the inductance threshold value,the embodiment is not limited thereto and the ratio may be differentlydefined according to the design of those skilled in the art.

For example, the controller 680 may determine that the foreign object ispresent if the quality factor value stored previously (measured beforethe ping phase) is less than the determined quality factor thresholdvalue or the pre-stored inductance value is less than the determinedinductance threshold value.

The controller 680 may stop power transfer upon determining that theforeign object is present and perform control to output a predeterminedwarning alarm indicating that the foreign object has been detected. Forexample, the alarm unit may include, but is not limited to, a beeper, anLED lamp, a vibration element, a liquid crystal display, etc.

The reference quality factor value included in the FOD status packet maybe determined to be the smallest value of the quality factor valuescalculated in correspondence with the wireless power receiver at aspecific position of a charging bed of a specified wireless powertransmitter.

The inductance value included in the FOD status packet may be determinedto be the smallest value of the quality factor values calculated incorrespondence with the wireless power receiver at a specific positionof a charging bed of a wireless power transmitter specified for astandard performance test.

In addition, if the foreign object is detected in the negotiation phase,the controller 680 may return to the selection phase and control themeasurement unit 640 to calculate the quality factor value and theinductance value of the resonant circuit 630 at predetermined periods.At this time, the controller 680 may compare the quality factor valueand the inductance value acquired in a state of detecting the foreignobject with the predetermined quality factor threshold value and theinductance threshold value to determine whether the detected foreignobject has been removed from the charging area. In an additionalembodiment, upon determining that the foreign object has been removed,the controller 680 may perform control to enter the power transfer phaseand to resume charging of the wireless power reception apparatus. Atthis time, the controller may enter the power transfer phase whileskipping the identification and configuration phase and/or thenegotiation phase.

The demodulator 661 demodulates an in-band signal received from thewireless power reception apparatus and transmits the demodulated signalto the controller 680. For example, the demodulator 661 may demodulatethe packet of FIG. 10 and transmit the demodulated packet to thecontroller 680.

The sensing unit 670 may measure the voltage, current, power, impedanceand temperature of a specific terminal, a specific element and aspecific position of the foreign object detection apparatus 600 (or thewireless power transmission apparatus).

For example, the sensing unit 670 may measure the voltage/current of theDC-converted power and provide the measured voltage/current to thecontroller 680. In addition, the sensing unit 670 may measure theinternal temperature of the wireless power transmission apparatus andprovide the measured result to the controller 680 in order to determinewhether overheating has occurred. In this case, the controller 680 mayadaptively cut off power supplied from the power supply or powersupplied to the resonant circuit 630 based on the voltage/current valuemeasured by the sensing unit 670. Therefore, a predetermined powercutoff circuit for blocking power supplied from the power supply 601 orDC power supplied to the inverter 620 may be further provided at oneside of the foreign object detection apparatus 600.

The sensing unit 670 may further include a Hall sensor, a pressuresensor, etc. In this case, the Hall sensor or the pressure sensor maydetect whether an object is present in the charging area, without beinglimited thereto.

The sensing unit 670 may detect change in current, voltage or impedanceof the resonant circuit 630 while the analog ping signal is transmittedin the selection phase to detect whether an object is present in thecharging area.

As described above, the foreign object detection apparatus 600 accordingto the embodiment may measure (or calculate) the quality factor value ofthe resonant circuit before entering the ping phase, when the object isdetected in the selection phase, and compare the threshold value (or thethreshold range) determined in the negotiation phase with the measuredquality factor value to determine whether the foreign object is present,thereby significantly reducing a probability of foreign object detectionfailure.

The sensing unit may be replaced with the measurement unit and thus maybe omitted.

In addition, the foreign object detection apparatus 600 according to theembodiment may dynamically determine the threshold value (or thethreshold range) for detecting the foreign object according to thereference quality factor value corresponding to the wireless powerreceiver, thereby performing foreign object detection optimized for thewireless power receiver.

For detailed operation of the remaining components shown in FIG. 6 b ,refer to the description of FIG. 6 a.

FIG. 7 a is a view illustrating the structure of an FOD status packetmessage according to an embodiment.

Referring to FIG. 7 a , the FOD status packet message 700 may have alength of 2 bytes and include a reserved field 701 having a length of 6bits, a mode field 702 having a length of 2 bits and a reference qualityfactor value field 703 having a length of 1 byte. All bits configuringthe reserved field 701 may be set to 0.

As denoted by reference numeral 704, if the mode field 702 is set to abinary value of “00”, this may mean that a reference quality factorvalue measured and determined in a state in which the wireless powerreceiver is powered off is recorded in the reference quality factorvalue field 703.

FIG. 7 b is a view illustrating the structure of an FOD status packetmessage according to an embodiment.

Referring to FIG. 7 b , the FOD status packet message 700 may have alength of 2 bytes and include a first data field 701 having a length of6 bits, a mode field 702 having a length of 2 bits and a referencequality factor value field 703 having a length of 1 byte.

As denoted by reference numeral 704, if the mode field 702 is set to abinary value of “00”, all bits configuring the first data field 701 areset to 0 and a reference quality factor value measured and determined ina state in which the wireless power receiver is powered off is recordedin the reference quality factor value field 703. In contrast, if themode field 702 is set to a binary value of “01”, the referenceinductance value measured and determined in a state in which a wirelesspower receiver is powered off is recorded in the first data field 701,and a reference quality factor value measured and determined in a statein which the wireless power receiver is powered off is recorded in thereference quality factor value field 703.

In the present embodiment, the foreign object detection apparatus (orthe wireless power transmission apparatus) may acquire at least one ofthe reference quality factor value and the reference inductance valuecorresponding to the wireless power receiver in the negotiation phase.

FIG. 7 c is a view illustrating the structure of an FOD status packetmessage according to an embodiment.

Referring to FIG. 7 c , the FOD status packet message 700 may have alength of 2 bytes and include a reserved field 701 having a length of 6bits, a mode field 702 having a length of 2 bits and a reference valuefield 703 having a length of 1 byte. All bits configuring the reservedfield 701 may be set to 0.

As denoted by reference numeral 704, if the mode field 702 is set to abinary value of “00”, a reference quality factor value measured anddetermined in a state in which the wireless power receiver is poweredoff is recorded in the reference value field 703. In contrast, if themode field 702 is set to a binary value of “01”, the referenceinductance value measured and determined in a state in which a wirelesspower receiver is powered off is recorded in the reference value field703.

In the present embodiment, the foreign object detection apparatus (orthe wireless power transmission apparatus) may acquire at least one ofthe reference quality factor value and the reference inductance valuecorresponding to the wireless power receiver in the negotiation phase.

FIG. 8 a is a diagram illustrating a status transition procedure forforeign object detection in a foreign object detection apparatusaccording to an embodiment.

Referring to FIG. 8 a , the foreign object detection apparatus maymeasure and store the quality factor value of the resonant circuit andthen enter the ping phase 810, when an object is detected in theselection phase 810. In the ping phase 820, the foreign object detectionapparatus may periodically transmit a predetermined power signal foridentifying the wireless power receiver, for example, a digital ping.

When a signal strength indicator corresponding to the digital ping isreceived in the ping phase 820, the foreign object detection apparatusmay enter the identification and configuration phase 830 to identify thewireless power receiver and to set various configuration parameters forthe identified wireless power receiver.

If identification and configuration of the wireless power receiver isterminated, the foreign object detection apparatus may enter thenegotiation phase 840 to receive the FOD status packet including thereference quality factor value.

The foreign object detection apparatus may determine a threshold value(or a threshold range) for determining whether a foreign object ispresent based on the reference quality factor value included in the FODstatus packet and compare the stored quality factor value with thedetermined threshold value (or threshold range) to determine whether aforeign object is present in the charging area.

As described in FIG. 6 a , in a wireless power receiver having a smallreference quality factor value, drop in the quality factor value fromthe reference quality factor value and a ratio of the quality factorvalue to the reference quality factor value when the foreign object isplaced in the charging area are relatively less than those of a wirelesspower receiver having a large reference quality factor value.Accordingly, the foreign object detection apparatus according to theembodiment may adaptively determine a threshold value (or thresholdrange) for detecting the foreign object according to the referencequality factor value received from the wireless power receiver.

Upon determining that the foreign object is present, the foreign objectdetection apparatus may stop power transfer and return to the selectionphase 810. In contrast, upon determining that the foreign object is notpresent, the foreign object detection apparatus may enter the powertransfer phase 850 to start wireless charging of the wireless powerreceiver.

FIG. 8 b is a diagram illustrating a status transition procedure forforeign object detection in a foreign object detection apparatusaccording to an embodiment.

Referring to FIG. 8 b , the foreign object detection apparatus maymeasure and store the quality factor value and the inductance value ofthe resonant circuit and then enter the ping phase 810, when an objectis detected in the selection phase 810. In the ping phase 820, theforeign object detection apparatus may periodically transmit apredetermined power signal for identifying the wireless power receiver,for example, a digital ping.

When a signal strength indicator corresponding to the digital ping isreceived in the ping phase 820, the foreign object detection apparatusmay enter the identification and configuration phase 830 to identify thewireless power receiver and set various configuration parameters for theidentified wireless power receiver.

If identification and configuration of the wireless power receiver isterminated, the foreign object detection apparatus may enter thenegotiation phase 840 to receive the FOD status packet including atleast one of the reference quality factor value and the referenceinductance value.

The foreign object detection apparatus may determine a threshold value(or a threshold range) for determining whether a foreign object ispresent based on the reference value(s) included in the FOD statuspacket and determine whether a foreign object is present in the chargingarea based on the determined threshold value (or threshold range).

Upon determining that the foreign object is present, the foreign objectdetection apparatus may stop power transfer and return to the selectionphase 810. In contrast, upon determining that the foreign object is notpresent, the foreign object detection apparatus may enter the powertransfer phase 850 to start wireless charging of the wireless powerreceiver. The foreign object detection apparatus may perform thecalibration phase 250 before entering the power transfer phase 850 asdescribed in FIG. 2 .

FIG. 9 a is a flowchart illustrating a foreign object detection methodin a wireless power transmission apparatus according to anotherembodiment.

Referring to FIG. 9 a , if an object is detected in the charging area inthe selection phase, the wireless power transmission apparatus maymeasure and store the quality factor value of the resonant circuit in apredetermined recording region (S901).

The wireless power transmission apparatus may determine whether aforeign object has been detected previously (S902).

If a foreign object has not been detected, the wireless powertransmission apparatus may enter the ping phase to wirelessly transmit adigital ping signal for identifying the wireless power receiver (S903).

The wireless power transmission apparatus may enter the identificationand configuration phase when a signal strength indicator is received inresponse to the digital ping signal, and transition to the negotiationphase when identification and configuration of the wireless powerreceiver is terminated (S904).

The wireless power transmission apparatus may determine a thresholdvalue (or threshold range) for determining whether a foreign object ispresent based on the reference quality factor value included in the FODstatus packet received in the negotiation phase (S905). Here, for themethod of determining the threshold value and the threshold range, referto the description of FIGS. 11 to 13 . The wireless power transmissionapparatus may wirelessly transmit a power signal having a predeterminedstrength in the negotiation phase.

The wireless power transmission apparatus may compare the stored qualityfactor value with the determined threshold value (or threshold range) todetermine whether a foreign object is present in the charging area(S906).

Upon determining that the foreign object is present, the wireless powertransmission apparatus may stop power transfer, and perform control tooutput a predetermined warning alarm indicating that the foreign objecthas been detected (S907 to S908). Thereafter, the wireless powertransmission apparatus may return to step 901.

Upon determining that the foreign object is not present in step 906, thewireless power transmission apparatus may enter the power transfer phaseto start charging of the wireless power receiver (S909).

Upon determining that the foreign object has been already detected instep 902, the wireless power transmission apparatus may determinewhether the detected foreign object has been removed from the chargingarea (S910). For the method of determining whether the detected foreignobject has been removed, refer to the description of FIGS. 6 a to 8 b.

Upon determining that the foreign object has been removed, the wirelesspower transmission apparatus may enter the power transfer phase toresume charging of the wireless power receiver.

Upon determining that the foreign object has not been removed in step910, the wireless power transmission apparatus may perform step 901.

FIG. 9 b is a flowchart illustrating a foreign object detection methodin a wireless power transmission apparatus according to anotherembodiment.

Referring to FIG. 9 b , if an object is detected in the charging area inthe selection phase, the wireless power transmission apparatus maymeasure and store the quality factor value and/or the inductance valueof the resonant circuit in a predetermined recording region (S901).

The wireless power transmission apparatus may determine whether aforeign object has been detected (S902).

Upon determining that the foreign object has not been detected, thewireless power transmission apparatus may enter the ping phase towirelessly transmit a digital ping signal for identifying the wirelesspower receiver (S903).

The wireless power transmission apparatus may enter the identificationand configuration phase when a signal strength indicator is received inresponse to the digital ping signal, and transition to the negotiationphase when identification and configuration of the wireless powerreceiver is terminated (S904).

The wireless power transmission apparatus may determine at least onethreshold value (or threshold range) for determining whether a foreignobject is present based on the FOD status packet received in thenegotiation phase (S905). Here, the threshold value may include aninductance threshold value and a quality factor threshold value. If thedetermined value is a threshold range, the threshold range may includean inductance threshold range and a quality factor threshold range. Thewireless power transmission apparatus may wirelessly transmit a powersignal having a predetermined strength in the negotiation phase.

The wireless power transmission apparatus may compare the stored valueswith the determined threshold value (or threshold range) to determinewhether a foreign object is present in the charging area (S906).

Upon determining that the foreign object is present, the wireless powertransmission apparatus may perform control to stop power transfer and tooutput a predetermined warning alarm indicating that the foreign objecthas been detected (optional) (S907 to S908). Thereafter, the wirelesspower transmission apparatus may return to step 901.

Upon determining that the foreign object is not present in step 906, thewireless power transmission apparatus may enter the power transfer phaseto start charging of the wireless power receiver (S909).

Upon determining that the foreign object has already been detected instep 902, the wireless power transmission apparatus may determinewhether the detected foreign object has been removed from the chargingarea (S910). Here, whether the detected foreign object has been removedfrom the charging area may be determined by comparing the quality factorvalue and the inductance value of the resonant circuit measured in step901 with the threshold value (or the threshold range) determined in step905, without being limited thereto.

Upon determining that the foreign object has been removed, the wirelesspower transmission apparatus may enter the power transfer phase toresume charging of the wireless power receiver.

Upon determining that the foreign object has not been removed in step910, the wireless power transmission apparatus may perform step 901.

As described above, the wireless power transmission apparatus accordingto the embodiment may measure (or calculate) the quality factor valueand inductance value of the resonant circuit before entering the pingphase, when the object is detected in the selection phase, and comparethe threshold value determined based on the FOD status packet in thenegotiation phase with the measured value to determine whether theforeign object is present, thereby significantly reducing theprobability of foreign object detection failure.

FIG. 10 is a graph of experimental results showing a degree of loweringa quality factor value as compared to a reference quality factor valueof each receiver type when a foreign object is placed in a charging areaaccording to an embodiment.

FIG. 10 shows an experimental result when a 10-cent coin is placed in acharging area.

As denoted by reference numerals 1010 and 1030 of FIG. 10 , it can beseen that, after placing the 10-cent coin in the charging area, anabsolute differential diff1 between a quality factor value and areference quality factor value increases as the reference quality factorvalue increases. At this time, a relationship between the quality factorNO_FO measured when the foreign object is not present, that is, thereference quality factor RFQ, and diff1 may be approximated by anequation denoted by reference numeral 1011. Although reference numeral1011 is approximated by a quadratic equation, this is merely an exampleand a linear equation, a higher order equation, an exponential equation,etc. may be used.

As denoted by reference numerals 1020 and 1030 of FIG. 10 , it can beseen that, after placing the 10-cent coin in the charging area, adifferential ratio % diff1 between a quality factor value and areference quality factor value increases as the reference quality factorvalue increases. At this time, a relationship between the quality factorNO_FO measured when the foreign object is not present, that is, thereference quality factor RFQ, and % diff1 may be approximated by anequation denoted by reference numeral 1021. Although reference numeral1021 is approximated by a quadratic equation, this is merely an exampleand a linear equation, a higher order equation, an exponential equation,etc. may be used.

FIG. 11 is a graph of experimental results showing a degree of loweringa quality factor value as compared to a reference quality factor valueof each receiver type when a foreign object is placed in a charging areaaccording to another embodiment.

FIG. 11 shows an experimental result when a 25-cent coin is placed in acharging area.

As denoted by reference numerals 1110 and 1130 of FIG. 11 , it can beseen that, after placing the 25-cent coin in the charging area, anabsolute differential diff2 between a quality factor value and areference quality factor value increases as the reference quality factorvalue increases. At this time, a relationship between the quality factorNO_FO measured when the foreign object is not present, that is, thereference quality factor RFQ, and diff2 may be approximated by anequation denoted by reference numeral 1111. Although reference numeral1011 is approximated by a quadratic equation, this is merely an exampleand a linear equation, a higher order equation, an exponential equation,etc. may be used.

As denoted by reference numerals 1120 and 1130 of FIG. 11 , it can beseen that, after placing the 25-cent coin in the charging area, adifferential ratio % diff2 between a quality factor value and areference quality factor value increases as the reference quality factorvalue increases. At this time, a relationship between the quality factorNO_FO measured when the foreign object is not placed, that is, thereference quality factor RFQ, and % diff2 may be approximated by anequation denoted by reference numeral 1121. Although reference numeral1021 is approximated by a quadratic equation, this is merely an exampleand a linear equation, a higher order equation, an exponential equation,etc. may be used.

As described above, the wireless power transmission apparatus accordingto the embodiment may measure (or calculate) the quality factor value ofthe resonant circuit before entering the ping phase, when the object isdetected in the selection phase, and compare the threshold valuedetermined based on the FOD status packet in the negotiation phase withthe measured value to determine whether the foreign object is present,thereby significantly reducing the probability of foreign objectdetection failure.

FIG. 12 is a view showing a result of measuring a quality factor valueand an inductance value of a resonant circuit according topresence/absence of a foreign object for each receiver type.

Reference numeral 1210 shows the inductance value Ls, resistance valueRs and quality factor value Q of the resonant circuit measured in astate 1211 in which nothing is placed in the charging area, a state 1212in which only a foreign object is placed, and a state 1213 in which onlya receiver is placed.

Reference numeral 1220 shows the inductance value Ls, resistance valueRs and quality factor value Q of the resonant circuit measured for eachreceiver type in a state in which a foreign object and a receiver aresimultaneously placed in the charging area.

As denoted by reference numeral 1211, the inductance value of theresonant circuit measured in a state (empty pad) in which nothing isplaced on the charging bed of the wireless power transmission apparatusis 25.20 pH and the quality factor value is 133.8.

As denoted by reference numeral 1210, if a foreign object including, forexample, FO #4 and a 10-cent coin is placed in a state in which nothingis placed in the charging area, the inductance value decreases. Incontrast, if a receiver capable of wirelessly receiving power, forexample, a smartphone having a wireless charging module, is placed in astate in which nothing is placed in the charging area, the inductancevalue increases.

In addition, as denoted by reference numeral 1210, if a foreign objector a receiver is placed in a state in which nothing is placed in thecharging area, the quality factor value decreases. In particular, it canbe seen that the quality factor values of Receiver 2 and Receiver 4 areless than the quality factor value of FO #4.

As denoted by reference numeral 1220, if standard foreign objects FO #4and a 10-cent coin are additionally placed in a state in which thereceiver is placed in the charging area, the inductance value and thequality factor value decrease as denoted by reference numerals 1221 and1222. However, the rate at which the inductance value and the qualityfactor value decrease is changed according to the type of the receiver.For example, as denoted by reference numeral 1213, 1221 and 1222, it canbe seen that, in the case of Receiver 1, if a foreign object isadditionally placed, change in quality factor value is greater thanchange in inductance value. Accordingly, in the case of Receiver 1,change in quality factor value may be detected rather than change ininductance value, in order to determine whether a foreign object ispresent. In contrast, it can be seen that, in the case of Receiver 4, ifa foreign object is additionally placed, change in inductance value isgreater than change in quality factor value. Accordingly, in the case ofReceiver 4, change in inductance value may be detected rather thanchange in quality factor value, in order to determine whether a foreignobject is present.

The type of the receiver placed in the charging area may be identifiedin the identification and configuration phase. Accordingly, the wirelesspower transmission apparatus may not identify the type of the receiverbefore entering the ping phase after the object is detected in theselection phase.

Accordingly, the wireless power transmission apparatus according toembodiment may measure and store the inductance value and quality factorvalue of the resonant circuit before entering the ping phase, when theobject is detected in the selection phase.

Thereafter, the wireless power transmission apparatus may determine theinductance threshold value and the quality factor threshold value fordetecting the foreign object based on the FOD status packet received inthe negotiation phase. The wireless power transmission apparatus maycompare the determined threshold value with the pre-stored inductancevalue and quality factor value to determine whether a foreign object ispresent.

For example, the wireless power transmission apparatus may finallydetermine that the foreign object is placed in the charging area, upondetermining that a foreign object is present by comparing the storedinductance value with the determined inductance threshold value or upondetermining that a foreign object is present by comparing the storedquality factor value with the determined quality factor threshold value.

Although the wireless power transmission apparatus determines thethreshold value for detecting the foreign object based on the FOD statuspacket in the above-described embodiment, this is merely an example andthe threshold range may be determined. In this case, the wireless powertransmission apparatus may determine that the foreign object is present,if at least one of the stored inductance value and the quality factorvalue is out of the determined threshold range.

The foreign object detection method of the wireless power transmissionapparatus according to another embodiment may further include receivinga received power strength packet for power calibration from the wirelesspower receiver. At this time, the received power strength packet mayinclude received power of the wireless power receiver corresponding to alight load or received power of the wireless power receivercorresponding to a load connection state.

FIG. 13 a is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 13 a , the FOD status packet message 1340 may have alength of 1 byte, and include an Operating Frequency for Maximum QualityFactor Value field 1340 having a length of 6 bits and a mode field 1342having a length of 2 bits.

The wireless power transmitter according to the embodiment may determinethat a foreign object is present in the charging area, if an operatingfrequency of a higher band, at which a quality factor value higher thana quality factor value measured at an operating frequency having amaximum quality factor value is measured, is present. Here, theoperating frequency of the higher band means a certain frequency greaterthan the operating frequency having a maximum quality factor value inthe operating frequency band.

The wireless power transmitter according to another embodiment maydetermine that a foreign object is present in the charging area, if aquality factor peak operating frequency (an operating frequency at whicha maximum quality factor value of the quality factor values measuredbefore the ping phase is measured) of a higher band than an operatingfrequency having the maximum quality factor value is present.

For example, an operating frequency 1341 for the maximum quality factorvalue may be an operating frequency for a maximum quality factor valuecorresponding to the type of the wireless power transmitter confirmed inthe identification and configuration phase 230 of FIG. 2 . For example,information on the operating frequency for the maximum quality factorvalue according to the type of the connectable wireless powertransmitter may be maintained in a predetermined recording region of thewireless power receiver. The operating frequency for the maximum qualityfactor value may vary according to the power class, design shape,manufacturer, and standard of the wireless power transmitter.

Accordingly, upon determining at which operating frequency or in whichoperating frequency range the maximum quality factor value is measuredin the wireless power receiver, the wireless power transmitter mayminimize the frequency range in which the quality factor value ismeasured in order to determine whether the foreign object is present.That is, the wireless power transmitter may not measure the qualityfactor value in a frequency band lower than the operating frequency forthe maximum quality factor value.

In another example, although the operating frequency 1342 for themaximum quality factor value is of a specific coil type, e.g., MP-A1type, defined in the WPC standard, the embodiment is not limited theretoand an operating frequency for a maximum quality factor valuecorresponding to the wireless power transmitter in which thetransmission coil is mounted may be used. Based on the MP-A1 type, thereceived maximum quality factor value may be scaled in consideration ofa design difference and product characteristics of different types ofwireless power transmitters and may be used to determine whether aforeign object is present.

The wireless power transmitter according to the embodiment may measureand store a quality factor value a1 in a specific upper-limit frequencyin an operating frequency band in the ping phase 220 (or before the pingphase) of FIG. 2 . Alternatively, a maximum quality factor of thequality factors measured in a predetermined frequency range (in theoperating frequency band) and a frequency, at which the maximum qualityfactor is measured, may be stored. Thereafter, the wireless powertransmitter may measure a quality factor value a2 at the operatingfrequency 1341 for the maximum quality factor value received through theFOD status packet 1340 in the negotiation phase 240, and determine thata foreign object is present in the charging area if a1 is greater thana2. Alternatively, the wireless power transmitter may compare theoperating frequency for the maximum quality factor value receivedthrough the FOD status packet 1340 in the negotiation phase 240 with thefrequency, at which the maximum quality factor measured in the pingphase 220 (or before the ping phase) is measured, thereby determiningwhether a foreign object is present.

If the frequency, at which the maximum quality factor measured in theping phase 220 is measured, is greater than the received maximum qualityfactor operating frequency, it may be determined that a foreign objectis present. This principle will be described below in detail.

Although the wireless power transmitter may measure only the qualityfactor value at the upper-limit frequency in the operating frequencyband in the ping phase 220 (or before the ping phase) in the presentembodiment, this is merely an example and both the quality factor valuesat the lower-limit frequency and the upper-limit frequency may bemeasured. In another embodiment, the quality factor value of eachfrequency may be measured through sweeping from the lower-limitfrequency to the upper-limit frequency.

In another embodiment, the quality factor value of each frequency may bemeasured through sweeping in a specific frequency region.

The wireless power transmitter is defined to measure the quality factorvalue at the lower-limit frequency in the operating frequency band inthe ping phase 220. Although the wireless power transmitter may measureonly the quality factor value at the upper-limit frequency in theoperating frequency band in the ping phase 220 in the presentembodiment, this is merely an example and both the quality factor valuesat the lower-limit frequency and the upper-limit frequency may bemeasured.

A frequency offset value from lower-limit frequency, that is, a lowestfrequency, in the operating frequency may be recorded in the operatingfrequency for the maximum quality factor value field 1341 according toan embodiment. At this time, an offset unit may mean, but is not limitedto, 10 kHz and may be less or greater than 10 kHz. For example, if theoperating frequency band of the wireless power transmitter is betweenthe lower-limit frequency of 100 kHz and the upper-limit frequency of300 kHz, the offset unit is 10 kHz, and the value recorded in theoperating frequency for the maximum quality factor value field 1341 is abinary value of 000011, the actual frequency for the maximum qualityfactor value may be 130 kHz (100 kHz+3*10 kHz).

In another embodiment, the wireless power transmitter may sweep theentire operating frequency band or a specific frequency band of theentire operating frequency band to measure the quality factor value,before the ping phase.

In another embodiment, instead of the field 1341 into which theoperating frequency for the maximum quality factor value of FIG. 13 a isinserted, an operating frequency value, at which the quality factorvalue is lower than the reference quality factor value by apredetermined value (or ratio), may be inserted into the field 1341.

The wireless power transmitter may compare the quality factor value B1measured at the reference operating frequency (for example, theoperating frequency for measuring the quality factor value is 100 kHz)in the ping phase 220 (or before the ping phase) with the quality factorvalue B2 measured at the operating frequency greater than the receivedoperating frequency, thereby determining whether a foreign object ispresent.

At this time, if B1 is greater than B2, it may be determined that aforeign object is present.

FIG. 13 b is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 13 b , the FOD status packet message 1350 may have alength of 2 bytes, and include an Operating Frequency for MaximumQuality Factor Value field 1351 having a length of 6 bits, a mode field1352 having a length of 2 bits, and a Reference Quality Factor Valuefield 1353 having a length of 1 byte.

Although the wireless power transmitter may check whether the operatingfrequency for the maximum quality factor value 1351 is included in theFOD status packet received through the value of the mode 1352, theembodiment is not limited thereto and the operating frequency for themaximum quality factor value 1351 may always be included in the FODstatus packet, regardless of the value of the mode 1352.

When the FOD status packet of FIG. 7 a is received, the wireless powertransmitter may compare the reference quality factor value with thequality factor value measured in the ping phase 220 (or before the pingphase) to determine whether a foreign object is present (Method 1) orcompare the operating frequency for the maximum quality factor valuewith the maximum operating frequency corresponding to the maximumquality factor value measured in the ping phase 220 (or before the pingphase) to determine whether a foreign object is present (Method 2, theembodiments of FIG. 13 a ).

Alternatively, it may be determined whether a foreign object is presentusing multiple methods.

In an embodiment, the wireless power transmitter may determine whether aforeign object is present using Method 1. At this time, two thresholdvalues (Threshold value 1:Q_Threshold 1 and Threshold value2:Q_Threshold 2) may be determined based on the received referencequality factor value.

If the quality factor value measured before the ping phase 220 is lessthan Threshold value 2, the wireless power transmitter may determinethat a foreign object is present.

If the quality factor value measured before the ping phase 220 is lessthan Threshold value 1 and is greater than or equal to Threshold value2, the wireless power transmitter may determine that a foreign object ispresent through Method 2.

FIG. 13 c is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 13 c , the FOD status packet message 1360 may have alength of 2 bytes, and include a wireless power transmitter (Tx) typefield 1361 having a length of 6 bits, a mode field 1362 having a lengthof 2 bits, and an Operating Frequency for Maximum Quality Factor Valuefield 1363 having a length of 1 byte.

Although the wireless power transmitter may check whether the wirelesspower transmitter type 1361 and the operating frequency for the maximumquality factor value 1363 are included in the FOD status packet receivedthrough the value of the mode 1362, the embodiment is not limitedthereto and the wireless power transmitter type 1361 and the operatingfrequency for the maximum quality factor value 1363 may always beincluded in the FOD status packet, regardless of the value of the mode1362.

For example, the wireless power transmitter type 1361 may be a value (apredetermined classification number) indicating a predeterminedtransmitter (Tx) design number for uniquely identifying the wirelesspower transmitter registered upon WPC (Qi) authentication.

In another example, the wireless power transmitter type 1361 may be apredetermined classification number for classifying wireless powertransmitters having common design features and performance features.

The wireless power transmitter according to the embodiment may determinethat a foreign object is present in the charging area, if an operatingfrequency of a higher band, at which a quality factor value higher thana quality factor value measured at an operating frequency having amaximum quality factor value is present, is present. Here, the operatingfrequency of the higher band means a certain frequency greater than theoperating frequency having a maximum quality factor value in theoperating frequency band.

The wireless power transmitter according to another embodiment maydetermine that a foreign object is present in the charging area, if aquality factor peak operating frequency (an operating frequency at whicha maximum quality factor value of the quality factor values measuredbefore the ping phase is measured) of a higher band than an operatingfrequency having the maximum quality factor value is present.

Hereinafter, for convenience of description, the reference qualityfactor value measured when a foreign object is not present is RQF_NO_FOand the quality factor value measured when a specific foreign object ispresent is QF_FO. For example, although a specific foreign object isForeign Object #4 (which may be used interchangeably with FO4, forconvenience of description), which is an aluminum disk having a diameterof 22 mm and a thickness of 1 mm, the embodiment is not limited theretoand any coin may be used.

The wireless power transmitter measures a current quality factor valuebefore the ping phase, that is, in the selection phase. The wirelesspower transmitter determines a quality factor threshold value fordetermining whether a foreign object is present, in consideration of thereference quality factor value received from the wireless power receiverin the negotiation phase, a production and measurement tolerance forconsidering the design difference of each transmitter, and accuracy ofthe reference quality factor.

The reference quality factor value means the smallest value of thequality factor values measured in five areas (center and four positionsto the left, right, up and down from the center by 5 mm) of the chargingareas of the test power transmitter (TPT), for example, an MP1 (MP-A1)type transmitter. The quality factor value actually measured in thecharging area may differ between the transmitters according to thedesign difference between MP1 which is the test power transmitter (TPT)and the commercial wireless power transmitter including the inductancevalue of the transmission coil. A tolerance for calibrating this isreferred to as a production and measurement tolerance.

For example, a drop value 1321 of the reference quality factor may bedetermined by subtracting a quality factor value measured when aspecific foreign object is present from the reference quality factorvalue corresponding to the wireless power receiver.

In another example, the drop value 1321 of the reference quality factormay be a ratio of the quality factor value measured when a foreignobject is present to a reference quality factor value measured when aforeign object is not present. In this case, the drop value 1321 of thereference quality factor may be an integer value calculated as apercentage (%) or calculated by dividing the percentage by a specificunit STEP_VALUE, without being limited thereto. For example, the dropvalue 1321 of the reference quality factor may be calculated by Equation1 below.[(RQF_NO_FO−QF_FO)/RQF_NO_FO]*100 or[((RQF_NO_FO−QF_FO)/RQF_NO_FO)*100]/STEP_VALUE  Equation 1

(here, *100 may be used to represent the value in % and may not beapplied to an actual value.)

The wireless power receiver may have a reference quality factor dropvalue which varies according to at least one of the manufacturer and theproduct type.

Accordingly, the wireless power transmitter according to an embodimentmay acquire the drop value of the reference quality factor from thedetected wireless power receiver and adaptively determine a qualityfactor threshold for determining whether a foreign object is present inconsideration of the drop value of the reference quality factor.

Therefore, according to the embodiment, it is possible to minimize aproblem in which heat is generated or power transfer efficiency issignificantly reduced due to non-detection of a foreign object locatedin a charging area.

FIG. 13 d is a view illustrating the structure of an FOD status packetmessage according to an embodiment.

Referring to FIG. 13 d , the FOD status packet message 1300 may have alength of 2 bytes and include a reserved field 1301 having a length of 6bits, a mode field 1302 having a length of 2 bits and a referencequality factor value field 1303 having a length of 1 byte.

All bits configuring the reserved field 1301 may be set to 0.

As denoted by reference numeral 1304, if the mode field 1302 is set to abinary value of “00”, this may mean that a reference quality factorRQF_NO_FO (first reference quality factor) value measured and determinedin a state in which the FO is not present is recorded in the referencequality factor value field 1303, and, if the mode field 1302 is set to abinary value of “01”, this may mean that a reference quality factorRQF_FO (second reference quality factor) value measured and determinedin a state in which the FO is present is recorded in the referencequality factor value field 1303.

FIG. 3 e is a view illustrating the structure of an FO status packetmessage according to one embodiment.

Referring to FIG. 13 e , the FO status packet message 1310 may have alength of 3 bytes and include a reserved field 1311 having a length of 6bits, a mode field 1312 having a length of 2 bits, a reference qualityfactor value 1313, and a reference quality factor value with foreignobject 1314.

All bits configuring the reserved field 1301 may be set to 0.

The operation mode of the power receiver, to which the reference qualityfactor value 1313 is applied, may be identified through the mode field1312. As denoted by reference numeral 1315, if the value of the mode1312 is a binary value of “00”, this indicates the reference qualityfactor value measured when the wireless power receiver is powered off.

The wireless power receiver may have the reference quality factor valuemeasured when a foreign object is not present and the reference qualityfactor value measured when a foreign object is present, which varyaccording to at least one of the manufacture and the product type.

The wireless power transmitter according to an embodiment may adaptivelydetermine a quality factor threshold for determining whether a foreignobject is present, in consideration of the reference quality factorvalue measured when a foreign object is not present and the referencequality factor value measured when a foreign object is present. This isbecause change in quality factor value based on whether a foreign objectis present or not may differ between receivers. Therefore, according tothe embodiment, it is possible to minimize a problem in which heat isgenerated or power transfer efficiency is significantly reduced due tonon-detection of a foreign object located in a charging area.

FIG. 13 f is a view illustrating the structure of an FO status packetmessage according to another embodiment.

Referring to FIG. 13 f , the FO status packet message 1120 may have alength of 2 bytes, and include a Drop Value of Reference Quality Factorfield 1321 having a length of 6 bits, a mode field 1322 having a lengthof 2 bits, and a Reference Quality Factor Value field 1323.

Here, the drop value 1321 of the reference quality factor may bedetermined based on the reference quality factor value 1223 measuredwhen a foreign object is not present and the quality factor valuemeasured when a specific foreign object is present (Quality Factor ValueWith Foreign Object).

The mode field 1322 may be used to indicate that the drop value of thereference quality factor 1321 is recorded in the reserved field 1301 ofFIG. 13 d . For example, as denoted by reference numeral 1324, if thevalue of the mode field 1322 is a binary value of “01”, this may meanthe drop value of the reference quality factor 1321 is recorded.However, this is merely an example and another value, e.g., a binaryvalue of “10” or a binary value of “11” of the mode field 1322 may beused to indicate that the drop value of the reference quality factor1321 is recorded.

However, if the value of the mode field 1322 is set to a value otherthan a binary value of “00” the reference quality factor value 1323 mayautomatically mean a value measured in a state in which the powerreceiver is powered off.

Although the format of the foreign object status packet is described asbeing identified by the mode, for convenience of description, in aspecific embodiment, the foreign object status packet shown in FIGS. 13d to 13 g may be used regardless of the mode.

FIG. 13 g is a view illustrating the structure of an FO status packetmessage according to another embodiment.

Referring to FIG. 13 g , the FO status packet message 1330 may have alength of 2 bytes, and include an Accuracy of Reference Quality Factorfield 1331 having a length of 6 bits, a mode field 1332 having a lengthof 2 bits, and a Reference Quality Factor Value field 1333.

Here, the accuracy of the reference quality factor 1331 may be atolerance of the reference quality factor value 1333 measured when aforeign object is not present. For example, the reference quality factorvalue, to which tolerance is applied, may be set to a rate increased ordecreased from the reference quality factor value 1333 received from thewireless power reception apparatus, without being limited thereto.

The accuracy of the reference quality factor 1331 may vary according toat least one of the manufacturer of the wireless power receiver and theproduct type. For example, the wireless power receiver of Company A andthe wireless power receiver of Company B may be different from eachother in accuracy of the reference quality factor value measured byinterworking with the same wireless power transmitter. Accordingly, thewireless power transmitter needs to acquire information on accuracy ofthe reference quality factor of each wireless power receiver, and aquality factor threshold value for determining whether a foreign objectis present may be determined in consideration of the accuracy of thereference quality factor. In addition, in the wireless powertransmitter, hereinafter, for convenience of description, a qualityfactor threshold for determining whether a foreign object is present isreferred to as FO_QF_THRESHOLD.

For example, as the result of testing the same wireless powertransmitter, the measured reference quality factor value of the wirelesspower receiver of Company A may be 100 and the measured referencequality factor value of the wireless power receiver of Company B may be70. In this case, the accuracy, e.g., +/−7% of the reference qualityfactor corresponding to the wireless power receiver Company B may be setto be greater than the accuracy, e.g., +/−10% of the reference qualityfactor corresponding to the wireless power receiver Company A. That is,the wireless power receiver of Company B may be set to have higher errorsensitivity than the wireless power receiver of Company A.

Accuracy of the quality factor may vary according to the configurationof the finished product in which the receiver is mounted. According to aPCB, a camera module, an antenna and other parts mounted in the finishedproduct, the quality factor measured when a foreign object is notpresent may be less than the quality factors of the other finishedproducts. If the finished product is located in the charging areatogether with a foreign object, change in quality factor value may beless than those of the other finished products, thereby requiring highermeasurement accuracy.

The mode field 1322 may be used to indicate that the accuracy of thereference quality factor 1331 is recorded in the reserved field 1301 ofFIG. 13 d . For example, as denoted by reference numeral 1334, if thevalue of the mode field 1332 is a binary value of “01”, this may meanthat the accuracy of the reference quality factor 1331 is recorded.However, this is merely an example and another value, e.g., a binaryvalue of “10” or a binary value of “11” of the mode field 1322 may beused to indicate that the accuracy of the reference quality factor 1331is recorded.

However, if the value of the mode field 1332 is set to a value otherthan a binary value of “00”, the reference quality factor value 1333 mayautomatically mean a value measured in a state in which the powerreceiver is powered off.

FIG. 14 is a flowchart illustrating an FOD method according to anotherembodiment.

Referring to FIG. 14 , in the negotiation phase, the wireless powerreceiver 1410 may transmit an FOD status packet including a secondreference quality factor value (Second Reference Quality Factor Value,RQF_FO) to the wireless power transmitter 1420 (S1401). At this time,the value of the mode value of the FOD status packet may be set to “01”.

The second reference quality factor value may be determined to be thesmallest value of the quality factor values measured at a plurality ofpoints in the charging area of a specific wireless power transmitter andmay be maintained in the wireless power receiver.

For example, the second reference quality factor value RQF_FO may bedetermined to be the smallest value of a first quality factor valuemeasured at the center where the transmission coil (primary coil) andthe reception coil (secondary coil) are well aligned in a state in whichthe FO is present near the wireless power receiver placed in thecharging area and second quality factor values measured while movingwith a constant distance offset, for example, +/−5 mm on the x-axis andthe y-axis, without being limited thereto, from the center withoutrotation of the wireless power receiver in a state in which the FO ispresent near the wireless power receiver. The second quality factorvalues may include a quality factor value measured at at least fourdifferent positions.

The wireless power transmitter 1420 may determine a threshold value forFO detection based on a design factor pre-stored in correspondence withthe wireless power transmitter 1420 and the received second referencequality factor value (S1403). Hereinafter, for convenience ofdescription, the second reference quality factor value corrected basedon the design factor is referred to as a corrected quality factorthreshold value Q_threshold_correct.

Since the second reference quality factor value is determined based onthe quality factor value measured at a specific wireless powertransmitter (hereinafter referred to as a wireless power transmitter fortest), a wireless power transmitter commercially manufactured by aspecific manufacturer (hereinafter referred to as a commercial wirelesspower transmitter, for convenience of description) may be different fromthe wireless power transmitter for test in terms of configuration andfeatures. Accordingly, the commercial wireless power transmitter and thewireless power transmitter for test may be different from each other interms of the quality factor value measured under the same conditions.Accordingly, the second reference quality factor value used as thethreshold value for FO detection in the embodiment of FIG. 20 needs tobe corrected in consideration of the configuration and features, thatis, the design factor, of the commercial wireless power transmitter.

For example, the design factor may be a correction constant determinedbased on at least one of power class corresponding to the commercialwireless power transmitter, the characteristics and arrangement of atransmission coil, a power control algorithm installed in a transmitter,power transfer loss, and the shape and structure of the wireless powertransmitter. However, the embodiment is not limited thereto and a valuecapable of correcting the measurement error of the quality factor valuerelative to the wireless power transmitter for test may be used.

The wireless power transmitter 1420 may measure a current quality factorvalue Q_current and compare the current quality factor value Q_currentwith a corrected quality factor threshold value Q_threshold_correct(S1403 to S1404).

For reference, the current quality factor value may be measured beforethe digital ping phase, immediately before the negotiation(renegotiation) phase or periodically.

If the current quality factor value Q_current is greater than or equalto the corrected quality factor threshold value Q_threshold_correct asthe result of comparison, the wireless power transmitter 1420 maydetermine that FO is not detected and transmit an ACK response to thewireless power receiver 1410 (S1405). At this time, the status of thewireless power transmitter 1420 may transition from the negotiation stepto the power transfer phase.

If the current quality factor value Q_current is less than the correctedquality factor threshold value Q_threshold_correct as the result ofcomparison of step 1401, the wireless power transmitter 1420 maydetermine that FO is detected and transmit a NAK response to thewireless power receiver 1410 (S1406). At this time, the status of thewireless power transmitter 1420 may transition from the negotiationphase to the selection phase.

FIG. 15 is a flowchart illustrating an FOD method according to anotherembodiment.

Referring to FIG. 15 , in the negotiation phase, the wireless powerreceiver 1510 may transmit first to second FOD status packets includinga Reference Quality Factor Value Q_reference to the wireless powertransmitter 1520 (S1501 to S1502).

Here, the first FOD status packet may include a first reference qualityfactor value RQF_NO_FO when the mode has a binary value of “00”. Thesecond FOD status packet may include a second reference quality factorvalue RQF_FO when the mode is 1, that is, a reference quality factorvalue determined based on the quality factor value measured in a statein which an FO is present in the charging area.

Here, the first reference quality factor value RQF_NO_FO is greater thanthe second reference quality factor value RQF_FO.

The first and second reference quality factor values may be respectivelydetermined based on the quality factor values measured in a state inwhich an FO is not present near the receiver and in a state in which anFO is present near the receiver. For example, the first and secondreference quality factor values may be the smallest values of thequality factor values measured at a plurality of points in the chargingarea of a specific wireless power transmitter for test.

The wireless power transmitter 1520 may determine a Quality FactorThreshold Rate Q_threshold_rate for FO detection based on the receivedfirst to second reference quality factor values (S1503).

Here, the quality factor threshold rate Q_threshold_rate may becalculated by dividing a difference between the first reference qualityfactor value RQF_NO_FO and the second reference quality factor valueRQF_FO by the first reference quality factor value RQF_NO_FO. Forexample, if the first reference quality factor value RQF_NO_FO is 80 andthe second reference quality factor value RQF_FO is 50, the qualityfactor threshold rate Q_threshold_rate may be (80-50)/80=0.375.

The wireless power transmitter may 1520 may measure the current qualityfactor value Q_current and calculate a quality factor decrease rateQ_decrease_rate based on the measured current quality factor value andthe first reference quality factor value RQF_NO_FO (S1404).

For reference, the current quality factor value may be measured beforethe digital ping phase, immediately before the negotiation(renegotiation) phase or periodically.

The wireless power transmitter 1520 may determine whether the qualityfactor decrease rate Q_decrease_rate is less than the quality factorthreshold rate Q_threshold_rate through comparison (51505).

Upon determining that the quality factor decrease rate Q_decrease_rateis less than the quality factor threshold rate Q_threshold_rate as theresult of comparison, the wireless power transmitter 1520 may determinethat an FO is not detected and transmit an ACK response to the wirelesspower receiver 1510 (S1506). At this time, the status of the wirelesspower transmitter 1520 may transition from the negotiation phase to thepower transfer phase.

Upon determining that the quality factor decrease rate Q_decrease_rateis greater than or equal to the quality factor threshold rateQ_threshold_rate as the result of comparison in step 1505, the wirelesspower transmitter 1520 may determine that an FO is detected and transmita NAK response to the wireless power receiver 1510 (S1507). At thistime, the status of the wireless power transmitter 1520 may transitionfrom the negotiation phase to the selection phase.

Although FO detection is performed by comparing the quality factordecrease rate Q_decrease_rate with the quality factor threshold rateQ_threshold_rate in the embodiment of FIG. 15 , this is merely anexample and the wireless power transmitter according to anotherembodiment may calculate a corrected quality factor threshold rateQ_threshold_rate_correct based on the design factor corresponding to thewireless power transmitter, and determine whether an FO is present inthe charging area by comparing the quality factor decrease rateQ_decrease_rate with the corrected quality factor threshold rateQ_threshold_rate_correct.

In another embodiment, the quality factor threshold value may bedetermined as follows.

The quality factor threshold value may be determined in consideration ofthe quality factor measurement error range (±10% (0.1*the referencequality factor value) of the received reference quality factor value orthe accuracy of quality factor value (FIG. 19 g )) and the transmittercharacteristics (transmitter type (design), manufacturer, product ormeasurement error, etc.).

FIG. 16 is a quality factor table according to an embodiment.

The quality factor table 1600 shown in FIG. 16 may be maintained in thememory of the wireless power transmitter. The wireless power transmittermay update the quality factor table 1600 based on the received FO statuspacket. For example, the quality factor table 1600 may include at leastone of a receiver identifier field 1601, a Latest Measured QualityFactor Value field 1602, a first reference quality factor value fieldRQF_NO_FO 1603, a second reference quality factor value field RQF_FO1604, and a corrected quality factor threshold value fieldQ_threshold_correct 1605.

Here, the receiver identifier 1601 may be configured by any one or acombination of a manufacturer code, a basic device identifier and anextended device identifier acquired in the identification andconfiguration phase. For example, the receiver identifier may beconfigured by, concatenating the manufacturer code and the basic deviceidentifier. In another example, the receiver identifier may beconfiguring by concatenating the manufacturer code, the basic deviceidentifier and the extended device identifier.

In the Latest Measured Quality Factor Value field 1602, a latestmeasured quality factor value may be recorded in correspondence with thereceiver identifier 1601. At this time, if charging of the wirelesspower receiver corresponding to the receiver identifier 1601 is normallyterminated or transitioning from the negotiation phase to the powertransfer phase is normally performed, the wireless power transmitter mayrecord the quality factor value measured in the negotiation phase in thequality factor table 1600.

In addition, if the FOD status packet is received in the negotiationphase, the wireless power transmitter may record at least one of thesecond reference quality factor value RQF_FO and the first referencequality factor value RQF_NO_FO included in the FOD status packet in thequality factor table 1600.

In addition, the wireless power transmitter may record the correctedquality factor threshold value Q_threshold_correct calculated for FOdetection in the first negotiation phase with the wireless powerreceiver in the quality factor table 1600.

If the wireless power receiver corresponding to the receiver identifierrecorded in the quality factor table 1600 is subsequently detected, thewireless power transmitter may detect an FO by referring to the qualityfactor table 1600.

The quality factor table 1600 according to another embodiment mayfurther include at least one of the drop value of the reference qualityfactor 1321 described in FIG. 13 f and the accuracy of the referencequality factor 1331 described in FIG. 13 d.

FIG. 17 is a block diagram illustrating the configuration of an FOdetection apparatus according to an embodiment.

The FO detection apparatus 1700 according to an embodiment may beinstalled or mounted in the wireless power transmitter.

Referring to FIG. 17 , the FO detection apparatus 1700 may include acommunication unit 1710, a determination unit 1720, a measurement unit1730, a detector 1740, a controller 1750 and a power transmission unit1760.

The communication unit 1710 may receive the FOD status packet includingthe reference quality factor value from the wireless power receiverconnected in the negotiation phase. Here, the reference quality factorvalue may include at least one of the reference quality factor valueRQF_NO_FO (the first reference quality factor value) when an FO is notpresent in the charging area and the reference quality factor valueRQF_FO (the second reference quality factor value) when an FO is presentin the charging area, and may be received through one FOD status packetor a plurality of FOD status packets in the negotiation phase.

The determination unit 1720 may determine a threshold value to be usedupon FO detection based on the received reference quality factor value.For example, the second reference quality factor value RQF_FO may bedetermined as the threshold value used upon FO detection, this is merelyan example and the second reference quality factor value corrected basedon the design factor corresponding to the wireless power transmitter maybe determined as the threshold value used upon FO detection.

As the threshold value used upon FO detection according to anotherembodiment, the quality factor threshold rate Q_threshold_ratecalculated based on the first and second reference quality factor valuesmay be determined.

In a first embodiment, the quality factor threshold rateQ_threshold_rate may be calculated by dividing a difference between thefirst reference quality factor value RQF_NO_FO and the second referencequality factor value RQF_FO by the first reference quality factor valueRQF_NO_FO. For example, if the first reference quality factor valueRQF_NO_FO is 80 and the second reference quality factor value RQF_FO is50, the quality factor threshold rate Q_threshold_rate may be(80-50)/80=0.375.

In a second embodiment, the quality factor threshold rateQ_threshold_rate may be a value obtained by dividing the secondreference quality factor value RQF_FO by the first reference qualityfactor value RQF_NO_FO. For example, if the first reference qualityfactor value RQF_NO_FO is 80 and the second reference quality factorvalue RQF_FO is 50, the quality factor threshold rate Q_threshold_ratemay be 50/80=0.625.

As the threshold value used upon FO detection according to anotherembodiment, a corrected quality factor threshold rateQ_threshold_rate_correct calculated based on a first corrected referencequality factor and a second corrected reference quality factorcalculated by applying a design factor predetermined according to thewireless power transmitter to the first and second reference qualityfactor values may be determined.

The measurement unit 1730 may measure or calculate a current qualityfactor value to be compared with the threshold value upon FO detection.

For example, the measurement unit 1730 may measure the current qualityfactor value Q_current in the negotiation phase.

In addition, the measurement unit 1730 may calculate the quality factordecrease rate Q_decrease_rate based on the measured current qualityfactor value Q_current and the first reference quality factor valueRQF_NO_FO. Here, the quality factor decrease rate Q_decrease_rate may becalculated by [RQF_NO_FO−Q_current]/[RQF_NO_FO].

In addition, the measurement unit 1730 may calculate the current qualityfactor rate Q_current_rate based on the measured current quality factorvalue Q_current and the first reference quality factor value RQF_NO_FO.Here, the current quality factor rate Q_current_rate may be calculatedby [Q_current]/[RQF_NO_FO].

The detector 1740 may compare the threshold value determined by thedetermination unit 1720 with the value measured or calculated by themeasurement unit 1730 to detect whether an FO is present in the chargingarea.

For example, the detector 1740 may determine that an FO is present inthe charging area if the current quality factor value Q_current is lessthan the second reference quality factor value RQF_FO, as shown in FIG.20 .

In another example, the detector 1740 may determine that an FO ispresent in the charging area if the current quality factor valueQ_current is less than the corrected quality factor threshold valueQ_threshold_correct, as shown in FIG. 14 .

In another example, the detector 1740 may determine whether an FO ispresent in the charging area, by comparing the quality factor decreaserate Q_decrease_rate with the quality factor threshold rateQ_threshold_rate, as shown FIG. 15 .

In another example, the detector 1740 may determine whether an FO ispresent in the charging area, by comparing the quality factor decreaserate Q_decrease_rate with the corrected quality factor threshold ratecalculated based on the design factor corresponding to the wirelesspower transmitter.

In another example, the detector 1740 may determine the quality factorthreshold value as follows.

The quality factor threshold value may be determined in consideration ofthe quality factor measurement error range (±10% (0.1*the referencequality factor value) of the received reference quality factor value orthe accuracy of quality factor value (FIG. 11 d )) and the transmittercharacteristics (transmitter type (design), manufacturer, product ormeasurement error, etc.).

The controller 1750 may control overall operation and input/output ofthe FO detection apparatus 1700. For example, the controller 1750 mayperform control, such that the status of the wireless power transmittertransitions from the negotiation phase to the power transfer phase andthe power transmission unit 1760 transmits power necessary to charge aload, if the FO is not detected by the detector 1740. In anotherexample, the controller 1750 may perform control, such that the statusof the wireless power transmitter transitions from the negotiation phaseto the selection phase and power transfer of the power transmission unit1760 is interrupted, if the FO is detected by the detector 1740.

The FO detection apparatus 1700 according to another embodiment mayfurther include a memory (not shown) for storing the quality factortable 1600 shown in FIG. 16 .

The FO detection apparatus 1700 according to another embodiment mayfurther include a correction unit (not shown) for calculating power lossbetween the wireless power receiver and the wireless power transmitterbefore transitioning to the power transfer phase, if the FO is notdetected by the detector 1740.

FIG. 18 is a flowchart illustrating an FOD method according to anotherembodiment.

Referring to FIG. 18 , in the negotiation phase, the wireless powerreceiver 1810 may transmit an FOD status packet including the referencequality factor value and the drop value of the reference quality factorto the wireless power transmitter 1820 (S1801). At this time, the modevalue of the FOD status packet may be set to “01”, without being limitedthereto.

Here, the reference quality factor value may be determined to be thesmallest value of the quality factor values measured at a plurality ofpoints of the charging area of a specific wireless power transmitterspecified for performance test and may be maintained in the wirelesspower receiver.

The wireless power transmitter 1820 may determine the quality factorthreshold value Q_threshold using the received reference quality factorvalue and the drop value of the reference quality factor (S1803).

For example, the wireless power transmitter 1820 may determine a valueobtained by subtracting the drop value of the reference quality factorfrom the reference quality factor value as a quality factor thresholdvalue, without being limited thereto. In another example, the qualityfactor threshold value may be determined using a predetermined qualityfactor value generation function using the reference quality factorvalue and the drop value of the reference quality factor as inputvariables.

The wireless power transmitter 1820 may measure the current qualityfactor value Q_current and determine whether the current quality factorvalue Q_current is greater than or equal to the quality factor thresholdvalue Q_threshold (S1803 to S1804).

For reference, the current quality factor value may be measured beforethe digital ping phase, immediately before the negotiation(renegotiation) phase or periodically.

If the current quality factor value Q_current is greater than or equalto the quality factor threshold value Q_threshold as the result ofcomparison, the wireless power transmitter 1820 may determine that FO isnot detected and transmit an ACK response to the wireless power receiver1810 (S1805). At this time, the status of the wireless power transmitter1820 may transition from the negotiation step to the power transferphase.

If the current quality factor value Q_current is less than the qualityfactor threshold value Q_threshold as the result of comparison in step1804, the wireless power transmitter 1820 may determine that FO isdetected and transmit a NAK response to the wireless power receiver 1810(S1806). At this time, the status of the wireless power transmitter 1820may transition from the negotiation phase to the selection phase.

FIG. 19 is a flowchart illustrating an FOD method according to anotherembodiment.

Referring to FIG. 19 , in the negotiation phase, the wireless powerreceiver 1910 may transmit an FOD status packet including accuracy ofthe reference quality factor and the reference quality factor value tothe wireless power transmitter 1920 (S1901). At this time, the modevalue of the FOD status packet may be set to a binary value of “01”,without being limited thereto.

The wireless power transmitter 1920 may determine the quality factorthreshold value Q_threshold using the received accuracy of the referencequality factor and the reference quality factor value (S1903).

The wireless power transmitter 1920 according to an embodiment maydetermine the quality factor threshold value using a pre-storedproduction and measurement tolerance.

For example, the wireless power transmitter 1920 may determine a valueobtained by subtracting the accuracy of the reference quality factor andthe production and measurement tolerance from the reference qualityfactor value as the quality factor threshold value, without beinglimited thereto. In another example, the quality factor threshold valuemay be determined using a predetermined quality factor threshold valuegeneration function using the accuracy of the reference quality factorand the reference quality factor value as input variables.

The wireless power transmitter 1920 may measure the current qualityfactor value Q_current and determine whether the current quality factorvalue Q_current is greater than or equal to the quality factor thresholdvalue Q_threshold (S1903 to S1904).

The current quality factor value according to an embodiment may bemeasured before the digital ping phase, immediately before thenegotiation (renegotiation) phase or periodically.

If the current quality factor value Q_current is greater than or equalto the quality factor threshold value Q_threshold as the result ofcomparison, the wireless power transmitter 1920 may determine that FO isnot detected and transmit an ACK response to the wireless power receiver1910 (S1905). At this time, the status of the wireless power transmitter1920 may transition from the negotiation step to the power transferphase.

If the current quality factor value Q_current is less than the qualityfactor threshold value Q_threshold as the result of comparison in step1904, the wireless power transmitter 1920 may determine that FO has beendetected and transmit a NAK response to the wireless power receiver 1910(S1906). At this time, the status of the wireless power transmitter 1920may transition from the negotiation phase to the selection phase.

The wireless power transmitter according to another embodiment mayacquire the reference quality factor value, the accuracy of thereference quality factor and the drop value of the reference qualityfactor through the plurality of FOD status packets. At this time, thewireless power transmitter may determine the quality factor thresholdvalue using at least one of the reference quality factor value, theaccuracy of the reference quality factor, the drop value of thereference quality factor and the production and measurement tolerance.

For example, the wireless power transmitter may determine the outputvalue of a predetermined quality factor threshold value generationfunction using the reference quality factor value, the accuracy of thereference quality factor and the drop value of the reference qualityfactor as input variables.

The wireless power transmitter according to another embodiment mayacquire the quality factor value, the accuracy of the reference qualityfactor and the drop value of the reference quality factor measured in astate in which a foreign object is not present from the wireless powerreceiver through a plurality of FOD status packets.

For example, the wireless power transmitter may determine a valueobtained by the accuracy of the reference quality factor and the dropvalue of the reference quality factor from the quality factor valuemeasured in a state in which a foreign object is not present, as thequality factor threshold value.

In another example, the wireless power transmitter may determine, as thequality factor threshold value, the output value of the predeterminedquality factor threshold value generation function using, as inputvariables, the quality factor value, the accuracy of the referencequality factor and the drop value of the reference quality factormeasured in a state in which a foreign object is not present.

FIG. 20 is a flowchart illustrating an FOD method based on a qualityfactor value according to another embodiment.

Referring to FIG. 20 , the wireless power transmitter may measure afirst quality factor value at a first frequency in a predeterminedoperating frequency band (S2001). Here, the operating frequency band maybe set to a frequency band from 100 kHz to 210 kHz in advance. However,this is merely an example and it should be noted that a differentoperating frequency band may be set according to at least one of thesettings and configuration of the wireless power transmitter and theapplied standard. Accordingly, step S2001 may be omitted and the qualityfactor value for a specific frequency may be measured in step S2003.

The wireless power transmitter may measure a second quality factor valueat a second frequency greater than the first frequency in the operatingfrequency band (S2003).

The wireless power transmitter may compare the first quality factorvalue with the second quality factor value (S2005).

In one embodiment, the first frequency may be an operating frequency fora maximum quality factor value (a peak Q factor value). In step S2005,the FOD status packet may be received in the negotiation phase, thefirst frequency may be confirmed, and the first quality factor valuecorresponding to the confirmed first frequency may be compared with thesecond quality factor value corresponding to the second frequencygreater than the first frequency.

In another embodiment, the first frequency may be 100 kHz. Since thewireless power transmitter and receiver may measure, transmit andreceive a reference quality factor value in a state of setting afrequency to 100 kHz, the first frequency may be 100 kHz.

If the first quality factor value is greater than the second qualityfactor value as a result of comparison, the wireless power transmittermay determine that the wireless power receiver is aligned and disposedin the charging area (S2007). Here, a high coupling coefficient betweena transmission resonant coil (primary coil) and a reception resonantcoil (secondary coil) may mean that the wireless power transmitter iswell aligned.

If the second quality factor value is greater than the first qualityfactor value as a result of comparison in step S2005, the wireless powertransmitter may determine that a foreign object is present in thecharging area and a misaligned wireless power receiver is present(S2009).

In another embodiment, if the first quality factor value is greater thanthe second quality factor value as a result of comparison in step S2005,it may be determined that only a foreign object is present in thecharging area.

When a foreign object is present, the quality factor value correspondingto the second frequency may be greater than the first quality factorvalue corresponding to the first frequency, as compared to the state inwhich the wireless power receiver is misaligned. The foreign objecthaving small influence may have a quality factor value similar to thatof the misaligned receiver, but a difference between the quality factorvalue measured when a foreign object having relatively large influenceis present and the quality factor value measured when the misalignedreceiver is present may be relatively large.

Upon determining that a foreign object is present or a misalignedwireless power receiver is present, the wireless power transmitteraccording to an embodiment may stop power transfer and output apredetermined alarm signal indicating that the foreign object is presentor the misaligned wireless power receiver is present.

The wireless power transmitter may enter the selection phase afterwaiting for a predetermined time after the alarm signal is output,thereby scanning the receiver again. The time waiting before enteringthe selection phase may be determined in consideration of a timerequired to remove the foreign object from the charging area by the useror to normally dispose the misaligned wireless power receiver again bythe user.

The wireless power transmitter according to another embodiment maymeasure the quality factor values corresponding to the first and secondfrequencies before entering the selection phase and compare the qualityfactor values to check whether the foreign object has been removed fromthe charging area. If the foreign object has been removed, the wirelesspower transmitter may enter the selection phase.

The wireless power transmitter according to another embodiment maymeasure the quality factor values corresponding to the first and secondfrequencies before entering the selection phase and compare the qualityfactor values to check whether the wireless power receiver has beenaligned. If the wireless power receiver has been aligned, the wirelesspower transmitter may enter the selection phase.

Although the wireless power transmitter according to an embodiment mayperform steps 2701 to 2709 in the selection phase 210 of FIG. 2 , thisis merely an example and steps 2701 to 2709 may be performed in anyphase performed before the negotiation phase 240, e.g., any one of theselection phase 210, the ping phase 220 and the identification andconfiguration phase 230.

The wireless power transmitter according to another embodiment mayperform steps 2701 to 2709 in the power transfer phase 260 of FIG. 2 .In this case, the wireless power transmitter may measure the qualityfactor values corresponding to the frequencies while power control usingoperating frequency control is performed and compare the quality factorvalues to determine whether a foreign object is present.

The wireless power transmitter according to another embodiment maydetermine (or acquire) a quality factor peak frequency, at which amaximum quality factor value is measured, in the predetermined operatingfrequency band (S2001, S2003). The frequencies in the predeterminedoperating frequency band (or a specific frequency band) may be swept tofind an operating frequency, at which the maximum quality factor valueis measured. The wireless power transmitter may receive an FOD statuspacket including a reference peak frequency from the wireless powerreceiver and compare the reference peak frequency with the acquiredquality factor peak operating frequency, determining whether a foreignobject is present. Direct comparison with the reference peak frequencymay be performed or a threshold frequency may be determined inconsideration of a transmission coil, design, product tolerance, etc.and the acquired quality factor peak operating frequency and thethreshold frequency may be compared.

FIG. 21 is a block diagram illustrating the structure of an FODapparatus corresponding to the embodiment of FIG. 20 .

Referring to FIG. 21 , the FO detection apparatus 2100 may include afirst quality factor measurement unit 2110, a second quality factormeasurement unit 2120, a detector 2130, an alarm unit 2140 and acontroller 2150. In another embodiment, the first quality factormeasurement unit and the second quality factor measurement may beunified into one module or device. In this case, the same measurementunit may measure the first quality factor value and the second qualityfactor value according to operating frequency control of the controller2150. Alternatively, the same measurement unit may measure a maximumquality factor value according to operating frequency control of thecontroller and store the quality factor peak operating frequencycorresponding to the maximum quality factor value in a memory.

The first quality factor measurement unit 2110 may measure the firstquality factor value corresponding to the first frequency in thepredetermined operating frequency band.

The second quality factor measurement unit 2120 may measure the secondquality factor value corresponding to the second frequency in thepredetermined operating frequency band. Here, the second frequency maybe greater than the first frequency and a difference between the firstfrequency and the second frequency may be determined based on thebandwidth of the operating frequency band, without being limitedthereto. For example, the first frequency and the second frequency maybe a lower-limit frequency and an upper-limit frequency of the operatingfrequency band.

The detector 2130 may determine whether a foreign object is present inthe charging area based on the first quality factor value and the secondquality factor value. Alternatively, it may be determined whether aforeign object is present in the charging area based on the qualityfactor peak operating frequency and the reference quality factor peakoperating frequency received from the wireless power reception unit.

For example, if the second quality factor value is greater than thefirst quality factor value, the detector 2130 may determine that aforeign object is present in the charging area or a misaligned wirelesspower receiver is present. In contrast, if the second quality factorvalue is less than the first quality factor value, the detector 2130 maydetermine that a foreign object is not present in the charging area oran aligned wireless power receiver is present.

In another example, if the second quality factor value is greater thanthe first quality factor value by a predetermined reference value, thedetector 2130 may determine that a foreign object is present in thecharging area or a misaligned wireless power receiver is present. Incontrast, if the first quality factor value is greater than the secondquality factor value of if a difference between the second qualityfactor value and the first quality factor value is less than apredetermined reference value, the detector 2130 may determine that analigned wireless power receiver is present.

In another example, the detector 2130 may determine whether a foreignobject is present in the charging area or a misaligned wireless powerreceiver is present, based on the change rate of the quality factorvalue according to change in frequency in the operating frequency band.

Although the change rate may be calculated by dividing a value obtainedby subtracting the first quality factor value from the second qualityfactor value by the first quality factor value, the embodiment is notlimited thereto and any equation capable of calculating the change rateof the quality factor value according to frequency change may be used.

If the calculated change rate is greater than 0 or is equal to orgreater than a first threshold value having a predetermined positivevalue, the detector 2130 may determine that a foreign object is presentin the charging area or a misaligned wireless power receiver is present.

In contrast, if the calculated change rate is less than 0 or is equal toor less than a second threshold value having a predetermined negativevalue, the detector 2130 may determine that an aligned wireless powerreceiver is disposed in the charging area.

If a foreign object or a misaligned wireless power receiver is detected,the detector 2130 may transmit the result of detection to the controller2150.

The alarm unit 2140 may output a predetermined alarm signal indicatingthat a foreign object is present in the charging area or a misalignedwireless power receiver is present in the charging area through an alarmelement, under control of the controller 2150. Here, the alarm elementmay include a buzzer, an LED lamp, a vibration element, and a liquidcrystal display, without being limited thereto.

Upon determining that a foreign object or a misaligned wireless powerreceiver is disposed, the controller 2150 according to an embodiment maycontrol the power transmission unit 2160 of FIG. 20 to stop powertransfer if power is currently transmitted and control the alarm unit2140 to output a predetermined alarm signal indicating that a foreignobject or a misaligned wireless power receiver is disposed.

The controller 2150 may enter the selection phase after waiting for apredetermined time after the alarm signal is output, and scan thereceiver again.

The time waiting before entering the selection phase may be determinedin consideration of a time required to remove the foreign object fromthe charging area by the user or to normally dispose the misalignedwireless power receiver again by the user.

The controller 2150 according to another embodiment may control thefirst to second quality factor measurement units 2110 and 2120 tomeasure the quality factor values corresponding to the first and secondfrequency before entering the selection phase, and compare the measuredfirst to second quality factor values to check whether the foreign hasbeen removed from the charging area. If the foreign object has beenremoved, the controller 2150 may enter the selection phase.

The controller 2150 according to another embodiment may perform controlto measure the quality factor values corresponding to the first andsecond frequencies before entering the selection phase and check whetherthe wireless power receiver has been normally aligned based on themeasured first to second quality factor values. If the wireless powerreceiver has been normally aligned, the controller 2150 may enter theselection phase.

In another embodiment, the foreign object detection phase may beperformed in the selection phase, that is, before the ping phase. Inthis case, if the foreign object is detected in the selection phase, thewireless power transmitter may enter the selection phase withoutentering the ping phase.

The controller 2150 according to another embodiment may temporarily stoppower transfer if a foreign object is detected while transmitting powerto the wireless power receiver, that is, in the power transfer phase 260of FIG. 2 , and output a predetermined alarm signal indicating that theforeign object has been detected. Upon determining that the detectedforeign object has been removed while outputting the alarm signal, thecontroller 2150 may perform control to resume power transfer.

FIG. 22 is a flowchart illustrating an FOD method based on a qualityfactor value according to another embodiment.

Referring to FIG. 22 , the wireless power transmitter may divide apredetermined operating frequency band into first to N-th frequencieshaving a predetermined frequency interval (S2201). Here, the operatingfrequency band may be roughly divided into a lower-limit frequency band,a middle frequency band and an upper-limit frequency band. It should benoted that the size of each frequency band may vary according to usersettings. For example, if the operating frequency band is from 100 kHzto 210 kHz and a frequency interval for distinguishing a specificfrequency in the operating frequency band is set to 10 kHz, theoperating frequency band may be divided into first to twelfthfrequencies. Here, first to third frequency may belong to thelower-limit frequency band (100 kHz to 130 kHz), fourth to ninthfrequencies may belong to the middle frequency band (130 kHz to 180kHz), and tenth to twelfth frequencies may belong to the upper-limitfrequency band (180 kHz to 210 kHz). This is merely an example and itshould be noted that a different operating frequency band and frequencyinterval may be set according to at least one of the settings andconfiguration of the wireless power transmitter and the appliedstandard.

The wireless power transmitter may calculate an average value a1 of thequality factor value(s) measured at (N−K+1)-th to N-th frequenciesincluded in the upper-limit frequency band (S2203).

In addition, the wireless power transmitter may calculate an averagevalue a2 of the quality factor value(s) measured at first to k-thfrequencies included in the lower-limit frequency band (S2205).

The wireless power transmitter may compare at with a2 (S2207).

If the quality factor average value a2 of the lower-limit frequency bandis greater than the quality factor average value at of the upper-limitfrequency band, the wireless power transmitter may determine that analigned wireless power receiver is disposed in the charging area(S2209). Here, a high coupling coefficient between a transmissionresonant coil (primary coil) and a reception resonant coil (secondarycoil) may mean that the wireless power transmitter is well aligned.

If a2 is less than or equal to a1 as the result of comparison in step2207, the wireless power transmitter may determine that a foreign objector a misaligned wireless power receiver is disposed in the charging area(S2211).

The wireless power transmitter may output a predetermined alarm signalindicating that the foreign object or the misaligned wireless powerreceiver is disposed in the charging area (S2213).

Although the wireless power transmitter according to an embodiment mayperform steps 2201 to 2213 in the selection phase 210 of FIG. 2 , thisis merely an example and steps 2701 to 2709 may be performed in anyphase performed before the negotiation phase 240, e.g., any one of theselection phase 210, the ping phase 220 and the identification andconfiguration phase 230.

The wireless power transmitter according to another embodiment mayperform steps 2201 to 2213 in the power transfer phase 260 of FIG. 2 .In this case, the wireless power transmitter may measure the qualityfactor values corresponding to the frequencies while power control usingoperating frequency control is performed. In addition, the wirelesspower transmitter may calculate the quality factor average value of theupper-limit frequency band and the quality factor average value of thelower-limit frequency band using the measured quality factor valuescorresponding to the frequencies and compare the quality factor averagevalues to determine whether a foreign object is present.

Although the quality factor average value a1 of the upper-limitfrequency band and the quality factor average value a2 of thelower-limit frequency band are compared to determine whether a foreignobject is present in the embodiment of FIG. 21 , this is merely anexample and the wireless power transmitter according to anotherembodiment may determine whether a foreign object or a misalignedwireless power receiver is disposed in the charging area based on theincrease/decrease in quality factor average value in addition to whetherthe quality factor average value increases or decreases according tofrequency change. For example, if a value obtained by subtracting a1from a2 is a negative number and an absolute value of a differencebetween a2 and a1 exceeds a predetermined threshold value, the wirelesspower transmitter may determine that a foreign object or a misalignedwireless power receiver is disposed in the charging area.

FIG. 23 is a block diagram illustrating the structure of an FODapparatus corresponding to the embodiment of FIG. 22 .

Referring to FIG. 23 , the FOD apparatus 2300 may include an operatingfrequency division unit 2310, a quality factor measurement unit 2320, anaverage calculator 2330, a detector 2340, an alarm unit 2350 and acontroller 2360.

The operating frequency division unit 2310 may divide a predefinedoperating frequency band into first to N-th frequencies, at which thequality factor value will be measured, at a predetermined frequencyinterval, and classify the divided frequencies into a lower-limitfrequency band, a middle frequency band and an upper-limit frequencyband. Here, the lower-limit frequency band and the number of frequenciesto be measured, which are included in the lower-limit frequency band,may be predefined and maintained in a predetermined recording region. Itshould be noted that the operating frequency band, the frequencyinterval, and the number of frequencies to be measured, which areincluded in the lower-limit/upper-limit frequency band, may be changedthrough a predetermined user interface mounted in the wireless powertransmitter and/or an external server connected to the wireless powertransmitter over a wired or wireless communication network.

The quality factor measurement unit 2320 may measure the quality factorvalues corresponding to the first to N-th frequencies. The qualityfactor measurement unit 2340 according to an embodiment may measure onlythe quality factor values corresponding to the frequencies to bemeasured, which are included in the lower-limit frequency band and theupper-limit frequency band.

The average calculator 2330 may calculate the average value a2 of thequality factor value(s) measured with respect to the lower-limitfrequency band and the average value a1 of the quality factor value(s)measured with respect to the upper-limit frequency band.

The detector 2340 may detect a foreign object or a misaligned wirelesspower receiver disposed in the charging area based on a1 and a2, andtransmit the result of detection to the controller 2360. For example, ifa value obtained by subtracting a2 from a1 is a positive number, thatis, if the average of the quality factor values increases as thefrequency in the operating frequency band increases, it may bedetermined that the foreign object or the misaligned wireless powerreceiver is present in the charging area. In contrast, if a valueobtained by subtracting a2 from a1 is a negative number, that is, if theaverage of the quality factor values decreases as the frequency in theoperating frequency band increases, it may be determined that an alignedwireless power receiver is present in the charging area.

In another example, the detector 2340 may determine whether a foreignobject or a misaligned wireless power receiver is present in thecharging area in consideration of the increase/decrease in qualityfactor average value in addition to whether the quality factor averagevalue increases or decreases according to frequency change in theoperating frequency band. For example, if a value obtained bysubtracting a1 from a2 is a negative number and an absolute value of adifference between a2 and a1 exceeds a predetermined threshold value,the wireless power transmitter may determine that a foreign object or amisaligned wireless power receiver is disposed in the charging area.

The alarm unit 2350 may output a predetermined alarm signal indicatingthat a foreign object is present in the charging area or a misalignedwireless power receiver is disposed in the charging area through analarm element, under control of the controller 2360. Here, the alarmelement may include a buzzer, an LED lamp, a vibration element, and aliquid crystal display, without being limited thereto.

FIGS. 24 a to 24 d are graphs of experimental results illustrating alogical basis of the embodiments of FIGS. 20 to 23 .

As denoted by reference numeral 2411 of FIG. 24 a , if only the firstreceiver is disposed in the charging area, the quality factor valuemeasured by the wireless power transmitter decreases as the frequency inthe operating frequency band (100 kHz to 210 kHz) increases. Incontrast, as denoted by reference numeral 2412, if the first receiverand a foreign object FO4 are disposed in the charging area, the qualityfactor value measured by the wireless power transmitter increases as thefrequency in the operating frequency band increases.

As denoted by reference numeral 2413, it can be seen that, w % ben onlythe first receiver is disposed in the charging area, the quality factorvalue measured at the operating frequency of 100 kHz is 44 and thequality factor value measured at the operating frequency of 210 kHz is40. In contrast, it can be seen that, when the first receiver and theforeign object FO4 are disposed in the charging area, the quality factorvalue measured at the operating frequency of 100 kHz is 27.1 and thequality factor value measured at the operating frequency of 210 kHz is30.5. Here, FO4 means a foreign object of the standard defined in theWPC standard.

The experimental result shown in FIG. 24 a shows that the quality factorvalue decreases as the frequency in the operating frequency bandincreases if the wireless power receiver is aligned and disposed in thecharging area, but increases as the frequency in the operating frequencyband increases if the foreign object is disposed in the charging area.

FIG. 24 b shows an experimental result of the second receiver generatedby a manufacturer different from that of the first receiver of FIG. 24a.

As denoted by reference numeral 2421 of FIG. 24 a , if only the secondreceiver is disposed in the charging area, the quality factor valuemeasured by the wireless power transmitter decreases as the frequency inthe operating frequency band (100 kHz to 210 kHz) increases. Incontrast, as denoted by reference numeral 2422, if the second receiverand a foreign object FO4 are disposed in the charging area, the qualityfactor value measured by the wireless power transmitter increases as thefrequency in the operating frequency band increases.

As denoted by reference numeral 2423, it can be seen that, when only thesecond receiver is disposed in the charging area, the quality factorvalue measured at the operating frequency of 100 kHz is 39.5 and thequality factor value measured at the operating frequency of 210 kHz is31.1. In contrast, it can be seen that, when the second receiver and theforeign object FO4 are disposed in the charging area, the quality factorvalue measured at the operating frequency of 100 kHz is 24.9 and thequality factor value measured at the operating frequency of 210 kHz is26.1.

The experimental result shown in FIG. 24 b shows that the quality factorvalue decreases as the frequency in the operating frequency bandincreases if the wireless power receiver is aligned and disposed in thecharging area, but increases as the frequency in the operating frequencyband increases if the foreign object is disposed in the charging area,equally to the experimental result of FIG. 24 a.

FIG. 24 c shows the quality factor value measured with respect to aforeign object FO4 and a 10-cent coin defined in the standard in theoperating frequency band.

Reference numerals 2431 and 2432 of FIG. 24 c show the change pattern ofthe quality factor value measured with respect to the 10-cent coin andFO4. As denoted by reference numerals 2431 and 2432, it can be seenthat, if a foreign object other than the wireless power receiver isplaced in the charging area, the quality factor value increases as thefrequency in the operating frequency band increases.

In the case of the 10-cent coin, some quality factor values measured inthe middle frequency band is greater than the quality factor valuemeasured in the upper-limit frequency band. Accordingly, in order tominimize erroneous determination occurring according to erroneousmeasurement result, as described in FIGS. 22 to 23 , it may bedetermined whether a foreign object is present based on the qualityfactor average value calculated in each of the lower-limit frequencyband and the upper-limit frequency band.

FIG. 24 d shows an experimental result of a third receiver manufacturedby a manufacturer different from those of the first to second receivers.

As denoted by reference numeral 2441 of FIG. 24 d , if only the thirdreceiver is placed in the charging area, the quality factor valuedecreases as the frequency increases. However, as denoted by referencenumerals 2442 to 2443, if a foreign object, e.g., FO4 or the 10-centcoin, is further placed in the charging area, the quality factor valueincreases as the frequency increases.

FIG. 24 e shows an experimental result of the standard wireless powertransmitter and the standard wireless power reception module used forproduct authentication.

As denoted by reference numeral 2452 of FIG. 24 e , it can be seen that,if the standard wireless power reception module is in the standardwireless power transmitter, the quality factor value decreases as thefrequency in the operating frequency band increases. Of course, asdenoted by reference numeral 2451, it can be seen that, even if nothingis placed in the charging area of the standard wireless powertransmitter, the quality factor value decreases as the frequency in theoperating frequency band increases. However, as denoted by referencenumeral 2453, it can be seen that the quality factor value measured in astate in which the standard wireless power reception module is placed inthe charging area of the standard wireless power transmitter decreasesto a certain extent as compared to the case where nothing is placed inthe charging area.

FIG. 25 is a view illustrating a relationship between a quality factorvalue and a maximum quality factor peak frequency according to placementof a foreign object and a wireless power receiver in a charging area ofa wireless power transmitter.

The table shown in FIG. 25 shows the shift of the maximum quality factorpeak frequency when the wireless power receiver and the foreign objectare placed in the charging area as compared to the case where only thewireless power receiver is placed in the charging area. At this time, itmay be determined whether a foreign object is present using the maximumquality factor peak frequency.

The wireless power transmitter may receive information on the referencequality factor peak frequency from the wireless power receiver anddetermine a threshold frequency based on the received information. Here,the threshold frequency may be determined in consideration of the designof a coil, circuit characteristics, tolerance, etc. The wireless powertransmitter may determine whether a foreign object is present, bycomparing the threshold frequency with the peak frequency of FIG. 25 .

FIG. 26 is a view illustrating a state transition procedure fordetecting a foreign object in a foreign object detection apparatusaccording to an embodiment.

Referring to FIG. 26 , when an object is detected in the selection phase2610, the foreign object detection apparatus may measure the qualityfactor value of the resonant circuit at a plurality of operatingfrequencies (S2601). Although the number of operating frequencies, atwhich the quality factor value is measured, is 2 to 6, the embodiment isnot limited thereto and the number of operating frequencies may beincreased. The operating frequency, at which the quality factor value ismeasured, may be selected in a predefined operating frequency range tohave a predetermined frequency interval. For example, if the operatingfrequency range of the foreign object detection apparatus is from 100kHz to 220 kHz and the number of operating frequencies is 5, the valuesof the operating frequencies, at which the quality factor value ismeasured, may be 100 kHz, 130 kHz, 160 kHz, 190 kHz and 220 kHz.

The foreign object detection apparatus may determine whether a foreignobject is placed, that is, whether a foreign object is present, based onthe measured quality factor values (S2602).

For example, the foreign object detection apparatus may determine that aforeign object is present in the charging area, when the quality factorvalue increases as the operating frequency increases. In contrast, theforeign object detection apparatus may determine that a foreign objectis not present in the charging area, when the quality factor valuedecreases as the operating frequency increases.

In another example, the foreign object detection apparatus may calculatechange in quality factor value at adjacent operating frequencies anddetermine that a foreign object is present in the charging area when anaverage of the calculated changes exceeds a predetermined referencevalue. For example, the reference value may be 0, without being limitedthereto. Here, the adjacent operating frequencies mean two nearestoperating frequencies among the operating frequencies, at which thequality factor value is measured.

In another example, the foreign object detection apparatus may calculatethe slopes of the quality factor values at adjacent operatingfrequencies and may determine that a foreign object is present in thecharging area when the average of the calculated slopes exceeds apredetermined first reference value. In contrast, when the average ofthe calculated slopes is equal to or less than a predetermined secondreference value, it may be determined that a foreign object is notpresent in the charging area. The first reference value and the secondreference value may be different and, in this case, the first referencevalue is greater than the second reference value.

The foreign object detection apparatus may enter the ping phase 2620when the determination as to whether the foreign object is present isterminated.

In the ping phase 2620, the foreign object detection apparatus mayperiodically transmit a predetermined power signal for identifying thewireless power receiver, e.g., digital ping.

The foreign object detection apparatus may enter the identification andconfiguration phase 2630 when a signal strength indicator is received inthe ping phase 2620 and set various configuration parameters for theidentified wireless power receiver.

The foreign object detection apparatus may enter the negotiation phase2640 when the identification and configuration of the wireless powerreceiver is terminated and receive a foreign object detection (FOD)status packet from the identified wireless power receiver (S2603). Here,the foreign object detection status may include a reference qualityfactor value.

The foreign object detection apparatus may transmit a NAK responsesignal or an ACK response signal to the identified wireless powerreceiver according to the result of determination in step 2602 (S2604).At this time, the foreign object detection apparatus may not determine athreshold value (a threshold range) for determining whether a foreignobject is present based on the received foreign object detection statuspacket. If the foreign object is present as the result of determinationin step 2602, the foreign object detection apparatus may transmit theNAK response signal to the identified wireless power receiver andtransition to the selection phase 2610. At this time, the foreign objectdetection apparatus may stop power transfer and output a predeterminedwarning alarm indicating that the foreign object has been detected.

For example, if the foreign object is not present as the result ofdetermination in step 2602, the foreign object detection apparatus maytransmit the ACK response signal and then transition to the powertransfer phase 2650. In another example, the foreign object detectionapparatus may transition to the power transfer phase 2650 through thecalibration phase 250 of FIG. 2 , if the foreign object is not presentas the result of determination in step 2602.

The foreign object detection apparatus may enter the power transferphase 2650 to start wireless charging of the wireless power receiver.

The foreign object detection apparatus, which has transitioned to theselection phase 2610 according to foreign object detection, mayperiodically measure the quality factor values of the resonant circuitat a plurality of operating frequencies and determine whether theforeign object has been removed based on the measured quality factorvalues. Upon determining that the foreign object has been removed, theforeign object detection apparatus may enter the power transfer phase2650 to resume power transfer to the wireless power receiver. Incontrast, if the foreign object is not removed for a predetermined timeafter transitioning to the selection phase 2610 according to foreignobject detection, the foreign object detection apparatus may output apredetermined warning alarm indicating that the detected foreign objecthas not been removed.

The foreign object detection apparatus according to anther embodimentmay further transmit a predetermined foreign object (FO) presence statuspacket including FO status information corresponding to the result ofdetermination in step 2601 to the wireless power receiver. For example,if FO status information is “0”, this may mean that the foreign objectis not detected and, if FO status information is “1”, this may mean thatthe foreign object is detected, without being limited thereto.

In another embodiment, step S2603 may be omitted.

FIG. 27 is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 27 , the FOD status packet message 2700 may have alength of 2 bytes and include a first data field 2701 having a length of6 bits, a mode field 2702 having a length of 2 bits, and a referencequality factor value 2703 having a length of 1 byte.

As denoted by reference numeral 2704, if the mode field 2702 is set to abinary value of “00”, all bits of the first data field 2701 are set to 0and the reference quality factor value measured and determined in astate in which the wireless power receiver is powered off is recorded inthe reference quality factor value field 2703. In contrast, if the modefield 2702 is set to a binary value of “01”, an operating frequencyhaving the quality factor value measured in a state in which a wirelesspower receiver is powered off, which is lower than the reference qualityfactor value by 5%, is recorded in the first data field 2701. Thereference quality factor value measured and determined in a state inwhich a wireless power receiver is powered off may be recorded in thefirst data field 2701. For example, referring to FIG. 20 , the referencequality factor value of the receiver may be 39.5 which is measured whenthe operating frequency is 100 kHz. At this time, the quality factorvalue lower than the reference quality factor value by 5% is 37.525.Accordingly, the operating frequency having the quality factor valuelower than the reference quality factor value by 5% may be any valuebetween 120 kHz and 130 kHz.

Although the value corresponding to the operating frequency having thequality factor value lower than the reference quality factor value by 5%is recorded in the first data field 2701 in the embodiment of FIG. 27 ,this is exemplary and a value other than 5%, e.g., 7%, may be setaccording to the design of those skilled in the art.

FIG. 28 is a view illustrating a state transition procedure fordetecting a foreign object in a foreign object detection apparatusaccording to an embodiment.

Referring to FIG. 28 , when an object is detected in the selection phase2810, the foreign object detection apparatus may measure the qualityfactor value of the resonant circuit at a plurality of operatingfrequencies including the lower-limit frequency of the operatingfrequency band (S2801). Although the number of operating frequencies, atwhich the quality factor value is measured, is 2 to 8, the embodiment isnot limited thereto and the number of operating frequencies may beincreased. The operating frequency, at which the quality factor value ismeasured, may be selected in a predefined operating frequency range tohave a predetermined frequency interval. The embodiment is not limitedthereto and the operating frequencies may be arbitrarily selected in theoperating frequency range. For example, the operating frequency range ofthe foreign object detection apparatus may be from 100 kHz to 220 kHz.For example, if the lower-limit frequency is 100 kHz and the number ofoperating frequencies is 7, the values of the operating frequencies, atwhich the quality factor value is measured, may be 100 kHz, 120 kHz, 140kHz, 160 kHz, 180 kHz, 200 kHz and 220 kHz.

The foreign object detection apparatus may record the measured qualityfactor value of each operating frequency in a predetermined recordingregion.

The foreign object detection apparatus may enter the ping phase 2820, ifquality factor value measurement is terminated.

In the ping phase 2820, the foreign object detection apparatus mayperiodically a predetermined power signal for identifying the wirelesspower receiver, for example, digital ping.

When a signal strength indicator is received in the ping phase 2820, theforeign object detection apparatus may enter the identification andconfiguration phase 2830 to identify the wireless power receiver and toset various configuration parameters for the identified wireless powerreceiver.

If identification and configuration of the wireless power receiver isterminated, the foreign object detection apparatus may enter thenegotiation phase 2840 to receive the FOD status packet from theidentified wireless power receiver (S2802). Here, the foreign objectdetection status packet may include information on the operatingfrequency having the quality factor value lower than the referencequality factor value by 5% (hereinafter referred to as a thresholdfrequency, for convenience of description).

The foreign object detection apparatus may compare the quality factorvalue Q1 corresponding to the lower-limit frequency measured in step2801 with the quality factor value Q2 measured at an operating frequencygreater than the threshold frequency to determine whether a foreignobject is present (S2803). Here, Q2 may be a quality factor value havingthe largest value among the quality factor values measured at theoperating frequencies greater than the threshold frequency.

If Q2 is greater than Q1, the foreign object detection apparatus maydetermine that the foreign object is placed in the charging area. Incontrast, if Q2 is less than Q1, the foreign object detection apparatusmay determine that the foreign object is not placed in the chargingarea.

The foreign object detection apparatus according to another embodimentmay determine (or estimate) the quality factor value corresponding tothe threshold frequency based on the quality factor value of eachoperating frequency measured in step 2801. For example, if the samefrequency as the threshold frequency is included in the plurality ofoperating frequencies used to measure the quality factor value in step2801, the quality factor value measured at the operating frequencybecomes the quality factor value measured at the threshold frequency.However, if the same frequency as the threshold frequency is notincluded in the plurality of operating frequencies used to measure thequality factor value in step 2801, the quality factor valuecorresponding to the threshold frequency may be estimated based on atleast one quality factor value measured at an operating frequencyclosest to the threshold frequency. For example, a linear function maybe derived using the quality factor values measured at two operatingfrequencies closest to the threshold frequency and the quality factorvalue corresponding to the threshold frequency may be estimated bysubstituting the threshold frequency into the derived linear function,without being limited thereto.

The foreign object detection apparatus may transmit a NAK responsesignal or an ACK response signal to the identified wireless powerreceiver according to the result of determination in step 2803. At thistime, the foreign object detection apparatus may not determine athreshold value (a threshold range) for determining whether a foreignobject is present based on the received foreign object detection statuspacket. If the foreign object is present as the result of determinationin step 2803, the foreign object detection apparatus may transmit theNAK response signal to the identified wireless power receiver andtransition to the selection phase 2810. At this time, the foreign objectdetection apparatus may stop power transfer and output a predeterminedwarming alarm indicating that the foreign object has been detected.

For example, if the foreign object is not present as the result ofdetermination in step 2802, the foreign object detection apparatus maytransmit the ACK response signal and then transition to the powertransfer phase 2850. In another example, the foreign object detectionapparatus may transition to the power transfer phase 2850 through thecalibration phase 250 of FIG. 2 , if the foreign object is not presentas the result of determination in step 2803.

The foreign object detection apparatus may enter the power transferphase 2850 to start wireless charging of the wireless power receiver.

The foreign object detection apparatus, which has transitioned to theselection phase 2810 according to foreign object detection, mayperiodically measure the quality factor values of the resonant circuitat a plurality of operating frequencies and determine whether theforeign object has been removed based on the measured quality factorvalues. Upon determining that the foreign object has been removed, theforeign object detection apparatus may enter the power transfer phase2850 and resume power transfer to the wireless power receiver. Incontrast, if the foreign object is not removed for a predetermined timeafter transitioning to the selection phase 2810 according to foreignobject detection, the foreign object detection apparatus may output apredetermined warning alarm indicating that the detected foreign objecthas not been removed.

The foreign object detection apparatus according to anther embodimentmay further transmit a predetermined foreign object (FO) presence statuspacket including FO status information corresponding to the result ofdetermination in step 2801 to the wireless power receiver. For example,if FO status information is “0”, this may mean that the foreign objectis not detected and, if FO status information is “1”, this may mean thatthe foreign object is detected, without being limited thereto.

FIG. 29 is a view illustrating a state transition procedure fordetecting a foreign object in a foreign object detection apparatusaccording to an embodiment.

When an object is detected in the selection phase 2910, the foreignobject detection apparatus according to an embodiment may measure thequality factor values of the resonant circuit at a plurality ofoperating frequencies (S2901).

When the FOD status packet including the threshold phase is received,the foreign object detection apparatus may identify at least twooperating frequencies greater than or equal to the threshold frequencyand extract the measured quality factor values at the identifiedoperating frequencies (S2903).

The foreign object detection apparatus may compare the quality factorvalues corresponding to the operating frequencies greater than or equalto the threshold frequency to determine whether a foreign object ispresent (S2904). For example, if the quality factor value increases asthe operating frequency increases, the foreign object detectionapparatus may determine that the foreign object is present in thecharging area. In contrast, if the quality factor value decreases as theoperating frequency increases, the foreign object detection apparatusmay determine that the foreign object is not present in the chargingarea.

When an object is detected in the selection phase, the foreign objectdetection apparatus according to another embodiment may scan the qualityfactor value in the operating frequency band.

Here, the operating frequency band may be divided into a plurality oflower frequency regions which do not overlap. For example, the operatingfrequency band may be divided into a first frequency region includingthe lower-limit frequency and a second frequency region including theupper-limit frequency.

For example, if the operating frequency band is from 100 kHz to 200 kHz,the first frequency region is from 100 kHz to 150 kHz including thelower-limit frequency of 100 kHz and the second frequency region is from151 kHz to 200 kHz including the upper-limit frequency of 200 kHz.

The foreign object detection apparatus may scan the quality factorvalues while the frequency in the first frequency region is changed inpredetermined frequency units and identify the operating frequency (thefirst frequency), at which a highest quality factor value is measured.In addition, the foreign object detection apparatus may scan the qualityfactor values while the frequency in the second frequency region ischanged and identify the operating frequency (the second frequency), atwhich a highest quality factor value is measured. The foreign objectdetection apparatus may compare the quality factor value Q4corresponding to the first frequency with the quality factor value Q5corresponding to the second frequency to determine whether a foreignobject is present in the charging area. For example, if Q5 is greaterthan Q4, the foreign object detection apparatus may determine that theforeign object is present. In contrast, if Q5 is less than Q4, theforeign object detection apparatus may determine that the foreign objectis not present.

FIG. 30 is a view illustrating the structure of an FOD status packetmessage according to another embodiment.

Referring to FIG. 30 , the FOD status packet message 3000 may have alength of 2 bytes and include a reserved field 3001 having a length of 6bits, a mode field 3002 having a length of 2 bits, a first data field3003 and a second data field value 3004. Although the length of thefirst data field 3003 is 3 bits in the embodiment of FIG. 30 and thelength of the second data 3004 is 5 bits, this is merely an example andthe embodiment is not limited thereto. All bits of the reserved field3001 are set to 0.

As denoted by reference numeral 3005, if the mode field 3002 is set to abinary value of “00”, the reference quality factor value measured anddetermined in a state in which the wireless power receiver is poweredoff is recorded in the first data field 3003 and the second data field3004. In contrast, if the mode field 3002 is set to a binary value of“01”, information on the threshold frequency may be recorded in thefirst data field 3003 and information on a ratio of the quality factorvalue corresponding to the lower-limit frequency to the quality factorvalue corresponding to the threshold frequency may be recorded in thesecond data field 3004.

The method according to the foregoing embodiments may be implemented ascode that can be written to a computer-readable recording medium and canthus be read by a computer. Examples of the computer-readable recordingmedium include a ROM, a RAM, a CD-ROM, a magnetic tape, a floppy disk,an optical data storage, and a carrier wave (e.g., data transmissionover the Internet).

The computer-readable recording medium can be distributed over aplurality of computer systems connected to a network so thatcomputer-readable code is written thereto and executed therefrom in adecentralized manner. Functional programs, code, and code segmentsneeded to realize the embodiments herein can be construed by one ofordinary skill in the art.

Those skilled in the art will appreciate that the disclosure may becarried out in other specific ways than those set forth herein withoutdeparting from the spirit and essential characteristics of thedisclosure.

The above exemplary embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the disclosureshould be determined by the appended claims and their legal equivalents,not by the above description, and all changes coming within the meaningand equivalency range of the appended claims are intended to be embracedtherein.

The foreign object detection method according to the embodiment may beused in a wireless charging system for detecting a foreign objectlocated between a wireless power transmitter and a wireless powertransmitter using the quality factor value before the ping phase and inthe negotiation phase and the power transfer phase.

What is claimed is:
 1. A wireless power receiver, comprising: a transmitter configured to transmit to a wireless power transmitter, a foreign object detection status packet including a mode bit field indicating whether a foreign object detection status packet includes a reference peak frequency of the wireless power receiver, wherein the reference peak frequency is pre-assigned to the wireless power receiver; and a receiver configured to receive from the wireless power transmitter, a response indicating the foreign object is present or not present in a charging area of the wireless power transmitter, wherein the response is determined based on a comparison of a measured peak frequency of a power signal transmitted by the wireless power transmitter and an adaptable threshold frequency adapted based on the reference peak frequency included in the foreign object detection status packet from the wireless power receiver.
 2. The wireless power receiver according to claim 1, wherein the response indicates the foreign object is present in the charging area when the measured peak frequency of the power signal is greater than the adaptable threshold frequency.
 3. The wireless power receiver according to claim 1, wherein the response indicates the foreign object is not present in the charging area when the measured peak frequency of the power signal is equal to or less than the adaptable threshold frequency.
 4. The wireless power receiver according to claim 1, wherein the peak frequency of the power signal is shifted from the reference peak frequency when the foreign object is present in the charging area.
 5. The wireless power receiver according to claim 4, wherein the peak frequency of the power signal shifts to a lower frequency when the wireless power receiver is present in the charging area without the foreign object.
 6. The wireless power receiver according to claim 5, wherein the peak frequency of the power signal shifts to a higher frequency when the wireless power receiver is present in the charging area with the foreign object.
 7. The wireless power receiver according to claim 1, wherein the reference peak frequency includes a frequency corresponding to a Q-factor in an operating frequency range of the wireless power transmitter.
 8. The wireless power receiver according to claim 1, further comprising: a controller configure to suspend receiving a wireless power transmitted from the wireless power transmitter when the response indicates the foreign object is not present in the charging area.
 9. The wireless power receiver according to claim 1, wherein the reference peak frequency is a premeasured reference peak frequency with no foreign object present.
 10. The wireless power receiver according to claim 1, wherein the threshold value is determined by applying a design factor corresponding to the wireless power transmitter and a predefined tolerance.
 11. The wireless power receiver according to claim 1, wherein the reference peak frequency is pre-assigned to the wireless power receiver based on a reference wireless power transmitter.
 12. The wireless power receiver according to claim 11, wherein the adaptable threshold frequency is determined in consideration of at least one of a design of a coil and circuit characteristics being different with the reference wireless power transmitter.
 13. The wireless power receiver according to claim 1, wherein the controller is further configured to: controlling the transmitter to transmit the foreign object detection status packet at least once during a negotiation phase with the wireless power transmitter.
 14. The wireless power receiver according to claim 13, wherein a power transfer phase of wirelessly transmitting power to the wireless power receiver is not performed in response to the negotiation phase indicating the foreign object is present in the charging area. 